www.impactjournals.com/oncotarget/ Oncotarget, 2017, Vol. 8, (No. 58), pp: 99179-99202

Review Phosphodiesterase type 5 and cancers: progress and challenges

Ines Barone1, Cinzia Giordano2, Daniela Bonofiglio1, Sebastiano Andò1 and Stefania Catalano1 1Department of Pharmacy, Health and Nutritional Sciences, University of Calabria, Arcavacata di Rende, Italy 2Centro Sanitario, University of Calabria, Arcavacata di Rende, CS, Italy Correspondence to: Ines Barone, email: [email protected] Stefania Catalano, email: [email protected] Keywords: phosphodiesterase, cancer, targeted therapy, biomarkers, chemoprevention Received: June 20, 2017 Accepted: September 23, 2017 Published: October 12, 2017 Copyright: Barone et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License 3.0 (CC BY 3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. ABSTRACT Cancers are an extraordinarily heterogeneous collection of diseases with distinct genetic profiles and biological features that directly influence response patterns to various treatment strategies as well as clinical outcomes. Nevertheless, our growing understanding of cancer cell biology and tumor progression is gradually leading towards rational, tailored medical treatments designed to destroy cancer cells by exploiting the unique cellular pathways that distinguish them from normal healthy counterparts. Recently, inhibition of the activity of phosphodiesterase type 5 (PDE5) is emerging as a promising approach to restore normal intracellular cyclic guanosine monophosphate (cGMP) signalling, and thereby resulting into the activation of various downstream molecules to inhibit proliferation, motility and invasion of certain cancer cells. In this review, we present an overview of the experimental and clinical evidences highlighting the role of PDE5 in the pathogenesis and prevention of various malignancies. Current data are still not sufficient to draw conclusive statements for cancer patient management, but could provide further rational for testing PDE5- targeting drugs as anticancer agents in clinical settings.

INTRODUCTION measures, such as smoking control, vaccination (for liver and cervical cancers), early detection, and promotion of The current global demographic, epidemiologic and healthy behaviors. Moreover, the burden of suffering nutritional transitions signal an enormous cancer burden and premature deaths can be decreased through the use on society in countries of all income levels. The incidence of an appropriate therapy and palliative care [2]. Surgery, of cancer cases is on continuing growth also because of chemotherapy and radiotherapy are currently the three an increasing prevalence of established risk factors, such major treatments to prolong the survival of the majority as tobacco use, excess body weight, physical inactivity, of cancer patients, but clinical improvements are often infection and changes in the reproductive patterns associated to undesirable side effects on normal cells connected with urbanization and economic development. or tissues. Thus, as the biology of cancer has become Based on data from GLOBOCAN 2012, an estimated progressively understood on a molecular level, therapeutic 14.1 million new cancer cases and 8.2 million deaths were research has mainly shifted its focus from cytotoxic recorded in 2012 globally [1]. Breast and lung cancers oncology drugs to newer target-based agents able to inhibit represent the most frequently diagnosed cancers and specifically tumor outgrowth and progression mechanisms the leading causes of cancer death in women and men, or enhance host immune responses against cancer cells. respectively, in the world and in less developed countries. On the other hand, clinical trials and meta-analyses have Other frequently diagnosed cancers worldwide include demonstrated that simultaneous or sequential multi- those of the prostate, liver, stomach, and colorectum modal therapies may improve patient outcome, may have among males and those of the stomach, cervix uteri, and acceptable tolerability profiles and may be active against a colorectum among females. A substantial proportion of variety of tumor types as compared with a single-modality cases can be prevented by broadly adoption of effective therapy [3–6]. In the search of molecularly targeted www.impactjournals.com/oncotarget 99179 Oncotarget cancer therapy, tremendous interest has been given to the intracellular sites, organelles and membranes as well as expression and regulation of the phosphodiesterase type 5 for their incorporation into particular multimolecular (PDE5) as an important signaling modulator involved in regulatory complexes or signalosomes. The regulatory diverse aspects of tumor cell function. In the last decade, regions contain domains that can be subjected to diverse a significant number of studies have reported an increased types of modification (e.g., phosphorylation by various expression of PDE5 in several human cancers compared protein kinases), or sites that may interact with allosteric to normal or surrounding non-neoplastic tissues [7–10]. ligands (e.g., cGMP binding sites), selective effectors Concomitantly, PDE5 inhibitors have been examined (e.g., Ca2+/calmodulin), protein partners (e.g., RAF1), in multiple malignancies and cancer cell lines for their or molecular scaffolds (e.g., caveolin). In addition, direct anticancer activities, for their efficacy as chemo- N-terminal regulatory regions include dimerization sensitizers and for cancer chemoprevention (reviewed in domains and autoinhibitory modules as several PDEs exist [11, 12]). In this review, we will highlight the emerging as asymmetric homo- or heterodimers (e.g., in PDEs 1, 4, knowledge and our recent findings showing the role of and 5). Informations from the crystal structures of isolated PDE5 as a tumor biomarker as well as a potential target for catalytic cores of PDEs have revealed that these domains therapeutic strategies aimed at controlling and eventually exhibit the same topography, composed of aminoacids curing malignant diseases. First, we will briefly discuss folded into 16 helices [73]. The active site forms a deep the structure and the biological function of PDE5. Next, hydrophobic pocket that includes a histidine-rich PDE we will summarize the significance of PDE5 expression signature sequence motif and consensus metal binding on different cancer types in clinical settings as well as domains, represented by two Zn2+ binding motifs (motifs A

in experimental cellular and animal models. The benefit and B – HX3HXnE/D) and an additional binding site whose of targeting PDE5 in cancer prevention or treatment will metals could be Mg2+, Mn2+ or Co2+ [73, 74]. In addition to be also discussed because of the numerous advantages of the conserved portions important for cyclic nucleotide and PDE5 inhibitors. inhibitor bindings, the catalytic domain also encompasses variable determinants that are responsible of PDE family- The superfamily of PDEs related substrate affinities and selectiveness [75]. As expected from their complex genomic Mammalian cyclic nucleotide phosphodiesterases organization, multiple PDE isoforms are expressed in (PDEs) constitute a large and complex family of almost all cells (Table 1) [75, 76]. However, some cells are ubiquitously distributed hydrolases that have the unique relatively enriched in specific PDEs (e.g., photoreceptor function of catalysing the hydrolytic breakdown of cyclic PDE6 exclusively expressed in retina rods and cones and adenosine monophosphate (cAMP) and cyclic guanosine in the pineal gland) as well as some PDE alterations are monophosphate (cGMP) into the biologically inactive tightly connected to different pathological conditions (e.g., derivates 5′-AMP and 5′-GMP, respectively. The PDE PDE4B abnormalities have been linked to schizophrenia superfamily contains 11 distinct gene families (PDEs [77]) [75, 76, 78]. Recently, genetic alterations or 1 to 11), that encode at least 100 distinct PDE isoforms overexpression in PDE genes were described to be through alternative mRNA splicing, multiple promoters associated with tumor development. Polymorphisms in the and transcription start sites in human, rat, and mouse [13]. genes encoding PDE8A and PDE11A have been associated The 11 PDEs can be grouped into three broad categories with a predisposition to developing certain adrenocortical based on their sequence homology as well as substrate [79], testicular [69], and prostatic [70] cancers. More specificity and selectivity. PDE4, PDE7 and PDE8 are importantly, PDE5 overexpression has been reported in specific for cAMP hydrolysis; PDE5, PDE6 and PDE9 several types of cancers [7–10]. are specific for cGMP hydrolysis; PDE1, PDE2, PDE3, PDE10 and PDE11 exhibit dual specificity, acting on PDE5 structure, regulation, distribution, cAMP and cGMP with different affinities depending on signalling and function the isoform (Figure 1 and Table 1) [13–72]. The different PDEs are modular proteins sharing the following common The human PDE5A gene is located on chromosome structural organization from N-terminus to C-terminus 4q264,5 and contains about 23 exons spanning (Figure 1): 1) a highly divergent regulatory domain in approximately 100 kilobases, with the first three exons the N-terminal portion; 2) a conserved catalytic core of being alternative exons encoding the isoform-specific approximately 270 amino acids (~ 35–50% sequence 5’-ends of the PDE5 sequences [80, 81]. Cloning and homology); 3) a region of undetermined function that sequencing of the PDE5A gene showed that these can be prenylated (PDE6) or phosphorylated (PDE4) alternative exons are arranged in the order of A1-A3-A2 in the carboxyl terminus [19]. The N-terminal portions and are separated by an intron of 434 bp between A1 of PDE molecules contain structural determinants and and A3 and by another intron of 361 bp between A3 specific amino acid sequences that are responsible for and A2 [82, 83]. The human PDE5A gene promoter, localization of individual PDE isoforms to specific located upstream of the three isoform-specific first exons, www.impactjournals.com/oncotarget 99180 Oncotarget consists of a 139 bp core with full basal activity, a 308 GAF A and B (domains originally found to be present in bp upstream regulatory region, and a 156 bp downstream cGMP-regulated cyclic nucleotide PDEs, certain adenylyl regulatory region. Each of these two regulatory regions cyclases and the bacterial transcription factor FhlA [86]). could independently convey the responsiveness of The identified functions of these regions are cGMP- cAMP and cGMP to the core promoter and contained mediated allosteric regulation and dimerization of GAF- multiple consensus sites for several transcription factors, containing PDEs. Allosteric binding of cGMP facilitates including Sp1 [83, 84]. The weaker PDE5A2 promoter is phosphorylation of human PDE5 by protein kinase G 182 bp in length and contains one AP2- and three Sp1- (PKG) on serine 102 and this phosphorylation seems to binding sequences [84]. The upstream PDE5A promoter play a role in stabilizing the enzyme in its cGMP-bound is expected to direct the expression of all three PDE5 active state [87], increasing both its catalytic activity and isoforms, while the intronic PDE5A2 promoter can only cGMP-binding affinity [87–90]. In addition of functioning control the expression of the A2 isoform [85]. as negative feedback for cGMP signalling by activating Human PDE5A1 and A2 transcripts are found to the cGMP-specific PDE5, cGMP levels may influence also be expressed in almost all tissues, with PDE5A2 being the activity of non-selective PDE isoenzymes (e.g., PDE2 more common, and identifiable in almost all cells cultured or PDE3) and thereby modulate the crosstalk between from aortic smooth muscle, bladder smooth muscle, cyclic nucleotide pathways [91]. Modulation of cGMP urethra smooth muscle, penile smooth muscle, penile concentrations is accomplished by cAMP- and cGMP- endothelium, aortic endothelium, etc. On the contrary, the dependent activation of PDE2 and cGMP-dependent distribution of human PDE5A3 appears to be restricted activation of PDE5 [92–94]. cAMP may also increase to tissues with smooth and/or cardiac muscle component cGMP levels by inhibiting cGMP-degrading activities of [81]. The three PDE5A isoforms share similar cGMP- PDE1 and PDE3 [92]. Recently, Zhao et al. demonstrated catalytic activities and differ only in the N-terminal that amongst all PDEs, PDE2 and PDE5 compensate domain, in which no biochemical or physiological most strongly for the reduced activity of each other, an function has been identified. The N-terminal part of event that was indicated as strong coupling [95]. Indeed, PDE5 contains two regulatory GAF domains named as NO/cGMP/PKG activity potentiated by PDE5 inhibition

Figure 1: Common structure of the different PDE enzymes. The PDE superfamily contains 11 structurally-related gene families. Some PDEs are specific for cAMP or cGMP, and some exhibit dual substrate specificity. The N-terminal portion of the PDEs contains sequences important for cellular localization. The regulatory domain contains PDE-family specific sequences responsible of modulation of PDE enzymatic activities. The catalytic domain is present in the carboxy-terminal part of PDEs and is highly conserved. A and B indicate the two Zn2 + -binding motifs (HX3HXnE/D) that include invariant histidines and are critical to catalysis. HD, Hydrophobic domains.

www.impactjournals.com/oncotarget 99181 Oncotarget Table 1: PDE families and inhibitors Isozime Gene Substrate Regulation Major Tissue and Subcellular Functions Inhibitors References Family Members Specificity Cellular Expression Localization PDE1 A, B, C cAMP/ Ca2+/ Lung, heart, brain, Cytosolic/ Vascular smooth muscle contraction, Vinpocetine, IC224, [14–24] cGMP calmodulin smooth muscle, testis, perinuclear sperm function (PDE1A); IC86.340, SCH51866, sperm, macrophages, Dopaminergic signaling, immune cell 8-MeoM-IBMX, ITI-214 lymphocytes activation, and survival (PDE1B) Vascular smooth muscle cell proliferation, sperm function, neuronal signaling (PDE1C) PDE2 A cAMP/ cGMP-stimulated Adrenal cortex, lung, Membrane- Regulates aldosterone secretion, EHNA, BAY60–7550, [16, 21, 25–29] cGMP liver, platelets, heart, bound or phosphorylation of calcium channel in IC933, PDP, OXIDOLE brain, macrophages, cytosolic, heart, cGMP in neurons; endothelial endothelium mitochondria cell function under inflammatory conditions PDE3 A, B cAMP/ Phosphorylation/ Lung, heart, adipose Membrane- Cardiac contractility, platelet Milrinone, Tolafentrine, [21, 22, 29, 30–35] cGMP cGMP-inhibited tissue, adipocytes, bound or aggregation, vascular smooth muscle Enoximone, K-134, liver, smooth muscle, cytosolic contraction, oocyte maturation, renin Cilostazol, Cilostamide, kidney, hepatocytes, release (PDE3A) Trequinsin, OPC-33540 pancreatic beta Insulin signaling, cell cycle, cells, immune cells, proliferation (PDE3B) platelets PDE4 A, B, C, D cAMP Phosphorylation/ Broad, cardiovascular, Membrane- Brain function, monocyte and Cilomilast, Rolipram, [21, 22, 29, 32, 36–46] cAMP-specfic neural, immune and bound or macrophage activation, neutrophil Ro20–1724, Roflumilast, cGMP-insensitive inflammatory systems cytosolic infiltration, vascular smooth muscle AWD12281, V11294A, proliferation, fertility, vasodilatation, SCH35159, GSK256066, cardiac contractility Denbufylline, Arofylline, Apremilast PDE5 A cGMP Phosphorylation/ Broad, lung, Cytosolic Vascular smooth muscle contraction, Sildenafil, Taldanafil, [16, 21, 29, 47–57] cGMP-specific cerebellum, heart, platelet aggregation, cGMP signaling DA8159, Exisulind, cGMP-activated , brain, platelets, in brain E402, Vardenafil, vascular myocytes, Zaprinast, DMPPO, cardiac myocytes, Dipyridamole, gastrointestinal tissues Mirodenafil and penis PDE6 A, B, C, cGMP Phosphorylation/ Retina and pineal Cytosolic Phototransduction Avanafil, Udenafil, [29, 58–61] D, G cGMP-specific gland Zaprinast PDE7 A, B cAMP Transduction Heart, liver, kidney, Cytosolic Immune cell activation (PDE7A) ASB16165, BRL50481, [21, 22, 29] activated/ cAMP- brain, pancreas, Memory function and excreted T IC242, Dipyridamole, specific testis, spleen, skeletal (PDE7B) BMS-586353, muscle, immune cells Thiadiazoles PDE8 A, B cAMP cAMP-specfic Broad, testis, liver, Membrane- T-cell activation, sperm or Leydig Dipyridamole, PF- [29, 40, 62–64] Rolipram/IBMX heart, kidney, brain, bound or cell function, T4 and T3 production 04957325 insensitive skeletal muscle, cytosolic, (PDE8A) thyroid, spleen, colon, mitochondria ovary, immune cells PDE9 A cGMP cGMP-specific Broad, kidney, liver, Cytosolic or NO-cGMP signaling in brain BAY 73–6691, SCH- [21, 29, 65, 66] IBMX/insensitive lung, brain, spleen, nuclear 51866, WYQ C28L, PF- prostate, heart 04447943 PDE10 A cAMP/ Unknown Brain, heart, thyroid, Cytosolic or Learning and memory Papaverine, [16, 29, 67, 68] cGMP testis particulate Dipyridamole, PQ-10, TP-10, MP-10 PDE11 A cAMP/ Unknown Liver, prostate, testis, Cytosolic Sperm development and function None selective [62–72] cGMP salivary and pituitary gland

is partially compensated by PDE2 and reciprocally, of hypertrophy [98]. The authors demonstrated that compensatory increase in PDE5 cGMP rates is also the exogenous overexpression of each variant induced a greatest upon PDE2 inhibition. PDE5 inhibition indirectly sustained cell cycle progression in cardiomyocytes and also leads to a decrease in PDE3 cAMP hydrolysis rates fibroblasts transfected cells, with PDE5A3 isoform being [95]. It was also reported that cGMP is able to directly more efficient in the modulation of hypertrophic markers activate PDE5 without phosphorylation in response to respect to the other mPDE5A isoforms. sustained nitric oxide (NO) in the platelet [96]. Moreover, In catalysing the hydrolysis of cGMP, PDE5 plays small molecular mass proteins immunologically related to critical roles in controlling its intracellular levels, the the gamma subunit of PDE6 may prevent PKA-mediated compartmentalization of its signalling pathways and its activation of PDE5 in airway smooth muscle [97]. More downstream biological responses. cGMP signalling is recently, an elegant study revealed, for the first time in schematically shown in Figure 2. Briefly, cGMP activates mouse, the existence of three different PDE5A isoforms different pathways, resulting into the activation of cGMP- with similar biochemical features and different distribution dependent protein kinase G (PKG), cyclic nucleotide- patter and highlighted their potential role in the induction gated (CNG) ion channels, or certain cGMP-binding www.impactjournals.com/oncotarget 99182 Oncotarget PDEs, which lead to protein phosphorylation, ion fluxes, endothelium [102–104]; whereas it negatively impacts or cyclic nucleotide hydrolysis to affect gene expression or hypertrophy and contractility in cardiac myocardium other aspects of cellular activity [99]. An essential player [105, 106]. PDE5 has been also involved in the regulation in cGMP signaling is considered the serine/threonine of platelet aggregation [107], and in the improvement of protein kinase PKG, whose downstream substrates are learning and memory processes [108]. implicated in a variety of biological processes, including calcium homeostasis, platelet activation and adhesion, PDE5 inhibitors: selectivity and adverse effects smooth muscle contraction, cardiac function, vasodilation, cell differentiation, proliferation, and apoptosis [100, 101]. Since the discovery and characterization of PDE5, The most recognized function of PDE5A is the modulation a collection of molecules able to inhibit its enzymatic of vascular tone via regulation of intracellular cGMP and activity have been conceived. The first drugs, such as calcium levels, particularly in the lung and penis [75]. IBMX (3-isobutyl-1-methylxanthine), dipyridamole and Moreover, cGMP-PKG signalling pathway activation coffee, have been shown to be potent but non selective increases cell proliferation and permeability in the vascular inhibitors. Later, zaprinast was described as a more

Figure 2: Schematic representation of cyclic guanosine monophosphate (cGMP) signaling pathways. This graphic shows the basic synthetic, regulatory and downstream signalings that mediate the effects of endogenous cGMP in cells. Cyclic nucleotide phosphodiesterase type 5 (PDE5), which catalyzes the hydrolytic breakdown of cGMP into its biologically inactive derivative, regulates the amplitude and the duration of cGMP signalling. pGC, particulate Guanylyl Cyclase; sGC, soluble Guanylyl Cyclase; CNG-Ion channels, cyclic nucleotide-gated Ion channels; PKG, cGMP-dependent Protein Kinase or Protein Kinase G; MYTP, Myosin Phosphatase Targeting Subunit; MLCK, Myosin Light Chain Kinase; RGS2, Regulatory of G-coupled Signaling 2; ROCK, Rho-kinase. www.impactjournals.com/oncotarget 99183 Oncotarget specific molecule [109], but it did not find its application pulmonary vascular physiology observed in in vitro and into clinical practice. However, its chemical structure in vivo models of pulmonary hypertension following was used to design compounds with higher potency and PDE5 inhibition has provided the rationale to recommend selectivity, leading to the identification in 1989 of sildenafil also PDE5 as a target for the treatment of pulmonary (1-[4-ethoxy-3-(6, 7-dihydro-1-methyl–7-oxo-3-propyl- hypertension and respiratory distress [122, 123]. 1H-pyrazolo [4, 3-d]pyrimidin-5-yl) phenylsulphonyl]- At the present time, the orally administrated PDE5 4-methylpiperazine). Sildenafil, developed and marketed inhibitors sildenafil and tadalafil have Food and Drug as Viagra by Pfizer, showed a higher selectivity (> 1000 Administration approval for the treatment of ED as fold) for human PDE5 over PDE2, PDE3 and PDE4 and well as pulmonary arterial hypertension (PAH); whereas moderate selectivity (> 80 fold) over PDE1 [110]. On the vardenafil and avanafil are approved only for ED. contrary, this drug was shown to be only ~ 10 fold more However, a great number of papers published over the effective for PDE5 than retinal PDE6, explaining some last decade highlighted the potential clinical use of PDE5 blue tinting of vision reported as adverse effects after its inhibitors in other applications, for which current therapies use [111]. As a consequence, many companies designed are limited and in which the mechanism of action does other selective PDE5 inhibitors with reduced inhibitory not necessarily rely on their known vasodilatatory effects effects towards PDE6, including vardenafil (Levitra, [124]. Table 2 summarizes the medical conditions other Bayer-GSK), and tadalafil (Cialis, IC351, Lilly-ICOS), than ED and PAH that have shown consistent benefits which is 1000 fold less potent towards PDE6 [112]. These from treatment with these pharmacologic agents [124– compounds also interact with PDE11, with tadalafil being 196]. Importantly, reported adverse effects are generally the most potent of them in respect to vardenafil (IC50 = 73 mild, i.e. flushing, headache, backache, dyspepsia, and nM and IC50 = 840 nM, respectively), but the functional nasal congestion. Some users of sildenafil and vardenafil, consequences of these effects are still unknown [113]. that, as mentioned earlier, slightly inhibit photoreceptor Compared to sildenafil and vardenafil, tadalafil also PDE6, may also experience temporary and reversible provides a longer therapeutic effect due to its extended minimal visual disturbances. Therefore, as reported in half-life [114]. A low incidence of some PDE-related various reviews of pharmacotherapy, they represent a adverse events was then obtained with avanafil (Stendra, class of relative benign molecules in terms of safety and Vivus inc.) [115]. Indeed, this molecule, which acts more tolerability [197–199]. rapidly than other PDE5 inhibitors, showed a higher selectivity against non-PDE5 isozymes as following: i) ~ Links between PDE5 and selected cancers 6.5 fold greater than sildenafil and vardenafil for PDE6; ii) more than 27 fold compared to sildenafil for PDE1; iii) There has been a remarkable interest in identifying ~ 760 fold higher than tadalafil for PDE11. Other PDE5 new clinical use of PDE5 inhibitors as potent anticancer inhibitors, including udenafil, mirodenafil and lodenafil drugs with a novel mechanism of action (Figure 3). carbonate are currently under clinical investigation Since 2000, more than 150 papers have been reported [116–118]. It is important to underline that some PDE5 on the connection of PDE5 and different kind of tumors. inhibitors may also affect non-PDE proteins. Indeed, it Indeed, increased expression of PDE5 in various human has been shown that vardenafil was able to block calcium malignancies and the lack of such expression in normal channels in rabbit pulmonary arteries and human platelets cells have been described. In addition, PDE5 inhibitors [119], and sildenafil interacted with multidrug resistance have been examined for their direct inhibitory effects on protein 1 (MDR1; also known as ABCB1) and antigen tumor cell lines, for their ability to act as a sensitizers of peptide transporter 1 (APT1; also known as ABCB2) to cancer cells to chemotherapeutic agents, and as cancer block drug extrusion from cells [120]. This latter off- chemopreventive agents [12]. However, much of the target effect could be significant in reducing ABCB1- and research is preclinical, and only few clinical trials have ABCB2-mediated drug resistance and thus improving the been completed or are ongoing so far (http://www. efficacy of some chemotherapeutic agents, most probably clinicaltrials.gov). The list of the studies focused on the independently of PDE5 inhibition [120, 121]. effects of PDE5 inhibition in cancer patients is reported Data from reports using selective PDE5 inhibitors in Table 3. have been essential for a robust understanding of the cellular functions that are regulated by PDE5 in Lung cancer physiological states as well as under pathological conditions. For instance, sildenafil, originally designed as Lung cancer has emerged as the most common an antihypertensive molecule or a coronary vasodilator, cancer in the world, both in terms of new cases and deaths was shown to induce responses in off-target tissues, such (1.82 million diagnoses and 1.6 million deaths recorded in as in penis, changing the focus of this agent to erectile 2012) with the highest rates in Central/Eastern Europe and dysfunction (ED) and proposing PDE5 as a target for Eastern Asia [2]. Non-small cell lung cancers (NSCLCs) the treatment of ED. In addition, the improvement of represent more than 80% of all lung cancers [200]. Despite www.impactjournals.com/oncotarget 99184 Oncotarget Table 2: Proposed novel applications of PDE5 inhibitors Applications Conditions Agents References Male genitourinary dysfunctions Benign prostatic hyperplasia and Sildenafil, Tadalafil, Vardenafil, [125–130] lower urinary tract symptoms UK-369, 003 Peyronie’s disease Sildenafil [131–134] Priapism Sildenafil [135–137] Premature ejaculation, inability to Tadalafil, Sildenafil, Vardenafil [138–140] ejaculate Low sperm count or motility Tadalafil, Sildenafil, Vardenafil [141–145] Neurologic dysfunctions Neurogenesis and recovery from Tadalafil, Sildenafil [146–149] stroke Sildenafil [150–153] Cognitive functions Tissue and organ protection Antineoplastic agent toxicity Sildenafil [157–157] Gastrointestinal damage Sildenafil [158–160] Cutaneous Ulcerations Antiphospholipid syndrome Sildenafil [161] Scleroderma Sildenafil [162, 163] Refractory Raynaud’s Sildenafil [163–165] phenomenon Sildenafil [166, 167] Systemic sclerosis Transplant and reconstructive Heart transplant Sildenafil [168–170] surgery Liver transplant Sildenafil [171–174] Renal transplant Sildenafil [175] Lung transplant Sildenafil [176] Reconstructive surgery Sildenafil [177–178] Female genital dysfunctions Fertility Sildenafil [179–184] Pre-eclampsia Sildenafil [185–187] Diabetes Neuropathy and vasculopathy Sildenafil [188–191] Endothelium damage Sildenafil, Tadalafil [192–196]

current advances in chemotherapy treatment regimens, the anti-tumor effect of trastuzumab in a xenograft mouse response rates are still < 50%, and complete remissions model of lung cancer [207]. Another study showed that remain rare, highlighting the need of agents with novel sildenafil was able to enhance the anti-tumor effects of mechanisms of action to improve clinical outcomes. the standard of care drug pemetrexed in NSCLCs. In two Over the last years, the apoptotic and growth models of human NSCLC cells growing in athymic mice, inhibition activities of PDE5 inhibitors have been it was found that pemetrexed and sildenafil interacted in demonstrated in numerous lung cancer cell lines. Most an additive fashion to suppress tumor growth and this of the experiments were performed by using exisulind effect was further enhanced in vivo by co-treatment with (sulindac sulfone), a sulfone metabolite of the nonsteroidal the mTOR inhibitor temsirolimus [208]. The complex anti-inflammatory drug (NSAID) sulindac. Exisulind, molecular mechanisms by which these drug combinations which lacks the hallmark cyclooxygenase inhibitory induce lung cancer cell death were via increasing toxic activities of NSAIDs, acts as a cGMP PDE inhibitors, autophagosome formation, and through the activation causing a persistent increase in cellular cGMP, and of extant death receptors. More recently, Booth et al. inducing PKG [201–203]. It was previously demonstrated have evidenced how sildenafil enhanced the lethality of that the combination of exisulind with cytotoxic drugs pemetrexed and sorafenib, a potent inhibitor of chaperone resulted in a synergistic inhibition of human lung cancer ATPase activities, in multiple genetically diverse lung cell growth in culture [204]. In orthotopic lung cancer cancer cell lines and in xenografts of lung cancer in model systems, exisulind in association with docetaxel athymic nude mice [208]. significantly induced apoptosis, reduced tumor growth However, the clinical evidences do not support and metastasis, and increased survival [10, 205, 206]. experimental findings. In 2006, a phase I/II study was PDE5 inhibitors also improved the chemosensitivity of designed to evaluate the safety and efficacy of exisulind anti-cancer agents by increasing endocytosis-mediated in combination with gemcitabine as second-line therapy cellular drug uptake in lung cancer cells; for instance, in NSCLC patients whose disease progressed more than oral administration of the PDE5 inhibitor vardenafil 3 months from completion of first-line chemotherapy significantly increases the accumulation and enhances [209]. Although the primary endpoint of improving time www.impactjournals.com/oncotarget 99185 Oncotarget Table 3: List of the studies on PDE5 inhibitors and cancer at www.clinicaltrials.gov* Inhibitor Indication Status ClinicalTrials.gov# Sildenafil Pancreatic Cancer, Cholangiocarcinoma Phase 1 (recruiting) NCT02106871 Advanced Solid Tumors Bladder Cancer Phase 1 (recruiting) NCT02466802 Kidney Cancer Phase 2 (recruiting) NCT02422277 Breast, Gastrointestinal, Genitourinary, Phase 2 (completed) NCT01950923 Gynecological Cancers Phase 1 (active, not recruiting) NCT01375699 Non-small Cell Lung Cancer Phase 2, Phase 3 (completed) High-grade Glioma Phase 2 (recruiting) NCT00752115 Waldenstrom’s Macroglobulinemia Phase 2 (completed) NCT01817751 NCT00165295 Tadalafil Head and Neck Squamous Cell Carcinoma Phase 1 (recruiting) NCT02544880 Head and Neck Cancer Head and Neck Cancer Phase 2 (recruiting) NCT02544880 Head and Neck Squamous Cell Carcinoma Phase 3 (completed) NCT00843635 Multiple Myeloma Phase 2 (completed) NCT00894413 Multiple Myeloma Prostate Cancer Phase 2 (recruiting) NCT01858558 Pancreatic Cancer Phase 2 (terminated) NCT01374217 Phase 3 (completed) NCT00931528 Pancreatic Cancer Phase 1 (active, not recruiting) NCT01342224 Phase 1 (active, not recruiting) Primary Abdominal Malignancy Phase 1 (not yet recruiting) NCT01903083

NCT02998736 Vardenafil Glioma, Brain Neoplasms, Brain Metastasis Early Phase 1 (recruiting) NCT02279992 Udenafil Sigmoid Colon and Rectal Cancers Phase 2 (completed) NCT00607282

to progression was met, the overall survival outcome decreasing and men have been given hope for recovery of patients treated with the two drugs appears only of bladder and erectile function. Penile rehabilitation slightly better than other phase II studies of single-agent after prostatectomy often includes treatment with PDE5 gemcitabine. This may be likely due to suboptimal dosing inhibitors and accordingly, association between the effects of exisulind, or suboptimal scheduling or the lack of of these drugs and cancer recurrence have been examined functional interaction between exisulind and cytotoxic in different experimental and clinical studies. drugs despite the preclinical observations. Other phase II In support of PDE5 inhibitors’ ability to affect studies using exisulind in combination with chemotherapy prostate carcinogensis, it was reported that exisulind in advanced NSCLCs show no objective benefits regarding suppressed the growth of metastatic, human prostate both overall survival and time to progression compared cancer cells in a nude mouse xenograft model by with historic controls treated with chemotherapy alone increasing apoptosis [214]. In contrast, Qian et al. noted [210–212]. Disappointing results were also reported for that incontinuous oral administration of sildenafil citrate the combination of carboplatin, etoposide, and exisulind as was not able to influence primary tumor growth and initial therapy for patients with newly diagnosed extensive metastasis in an orthotopic prostate cancer model, most stage small cell lung cancers [213]. probably because cGMP elevation were only transient [215]. It was shown that sildenafil enhanced apoptosis and Prostate cancer antitumor efficacy of doxorubicin in mice bearing prostate tumor xenografts, while attenuating its cardiotoxic Prostate cancer represents the second most effects (i.e. left ventricular dysfunction) [216]. Next, frequently diagnosed solid malignancy among men the same research group investigated the mechanism worldwide, accounting for about 1.1 million cases in 2012 by which sildenafil may sensitize prostate cancer cell [1]. Fortunately, due to early detection and the nerve- to doxorubicin-mediated apoptosis, showing CD95 sparing prostatectomy, relative death rates have been (death receptor Fas)/FLIP (Fas-associated death domain www.impactjournals.com/oncotarget 99186 Oncotarget FADD) as key regulators of this event [217]. In 2016, by thereby thwart the emergence of more aggressive cancer in vitro cell culture and in vivo xenograft approaches, it phenotypes [222–224]. Another group also evaluated the was clearly demonstrated that PDE5/cGMP/PKG signal safety and efficacy of exisulind (twice daily for 12 months) targets to Hippo/TAZ pathway in maintaining stemness in delaying disease progression in men with rising prostate of prostate cancer stem cells, evidencing a novel role of specific antigen (PSA) levels after radical prostatectomy PDE5 in governing stem cell features [218]. Moreover, and found that exisulind inhibited the increase in PSA PDE5 was found to be mainly located in the stromal overall and prolonged PSA doubling time in high-risk compartment of the prostate, and accordingly tadalafil patients compared with placebo [225]. Contrary to these reduced proliferation of primary prostate stromal cells at a findings, using a large clinical database of patients with greater extent than of primary prostate basal epithelial cells prostate cancer (n = 4752) with a median follow-up of 60.3 [219]. Tadalafil also attenuated TGFβ1-induced fibroblast- months, it was shown that the use of PDE5 inhibitors after to-myofibroblast trans-differentiation, suggesting a radical prostatectomy may adversely impact biochemical potential value of PDE5 inhibitors in preventing stromal recurrence (BCR), defined as a PSA of 0.2 ng/ml or greater enlargement and treating benign prostatic hyperplasia and increasing after radical prostatectomy [226]. However, ([219] and reviewed in [220]). there are several limitations to this study, such as the lack A retrospective analysis including a total of 4974 of information on the type of the drug, the dose, the exact men revealed that the use of PDE5 inhibitors over a 7-year duration and frequency of use. Other authors retrospectively period was associated to a decreased incidence rate of performed a similar analysis of BCR in 2579 patients prostate cancer among men with ED compared to men with treated with bilateral nervesparing radical prostatectomy ED of the same age and with similar risk factors who were and showed that there was no association between PDE5 not treated with these agents [221]. It was hypothesized inhibitor use and an increased risk of BCR, regardless of the that a higher ejaculation frequency can protect against therapeutic regimen used [227]. prostate cancer development or alternatively vasodilation On the basis of these findings, there is no strong induced by PDE5 inhibition may counteract hypoxia and evidence to modify current clinical practice, and therapy

Figure 3: Proposed mechanisms underlying the anti-cancer activities of PDE5 inhibitors. PDE5 inhibitors may hamper tumor progression by activating downstream signaling pathways, mainly PKG-mediated ones, which induce apoptosis, autophagy, growth suppression, inhibition of angiogenesis and of stemness. PDE5 inhibitors may also enhance the therapeutic effectiveness of multiple anti- neoplastic agents by increasing intracellular accumulation of drugs and cGMP levels through the block of the substrate efflux function of ABC multidrug-resistant transporters. ABC transporter Efflux Pumps, ATP-binding cassette transporter Efflux Pumps; ROS, Radical Oxygen Species; HSP, Heat Shock Protein; GRB78, Glucose-Regulated Protein; JNK, c-Jun N-terminal kinases; ERK, Extracellular Signal- regulated Kinases; MST, Mammalian Ste20-like Protein Kinase; LAT, Large Tumor Suppressor Kinase; TAZ, Transcription Regulator Protein-1. www.impactjournals.com/oncotarget 99187 Oncotarget with PDE5 inhibitors still remains the more recommended PDE5 levels, highlighting a role for PDE5 in predicting option for many postprostatectomy patients for penile disease progression in ER-positive tumors that according rehabilitation programs [228]. to our immunohistochemistry analysis may have lower levels of the enzyme compared with ER-negative cases. Breast cancer In addition, since PDE5 retained its significance when performing a multivariate analysis including PDE5 Breast carcinoma is the most common malignancy expression, ER, HER2, and lymph node status in the and the leading cause of cancer-related death in women entire database, it is tempting to speculate that high PDE5 worldwide. Breast cancer is a complex and highly levels may independently predict poor outcome among heterogeneous disease classified on the basis of global patients with breast cancer. However, up to now, only one gene expression analyses into at least five biologically study was conducted to clinically evaluate the safety and different intrinsic subtypes (i.e. luminal A, luminal B, activity of PDE5 inhibitor in breast cancer. In particular, human epidermal growth factor receptor 2 (HER2)- it was demonstrated that administration of exisulind in enriched, basal-like, and normal-like) with distinct combination with capecitabine was well tolerated in a morphologic features, variable clinical outcomes and small number of patients with metastatic breast cancer disparate therapeutic responses [229]. (n = 35), but the synergism between these two drugs at the Increased PDE5 expression has also been reported doses tested appears to be modest [9]. in various cell lines deriving from breast cancer (MCF- 7, HTB-26, MDA-MB-468) [54], giving the rational Colorectal cancer to assess the anticancer effects of PDE5 inhibition. Indeed, the PDE5 inhibitor exisulind selectively exerted, Colorectal cancer is the third most commonly in various breast cancer cells, pro-apoptotic and anti- diagnosed cancer in men and the second in women proliferative effects concomitantly with elevation of worldwide, with an estimated 1.4 million cases and cGMP and activation of PKG, without effects on human 693,900 deaths occurring in 2012 [1]. In contrast to mammary normal epithelial cells [230]. Inhibition of incidence trends, decreasing colorectal cancer mortality PDE5 and activation of PKG by exisulind was associated rates have been observed in a large number of countries with reduced oncogenic Wnt/β-catenin-mediated and are most likely attributed to colorectal cancer transcriptional activity and subsequent downregulation screening, reduced prevalence of risk factors, and/ of target genes, including cyclin D1 and survivin [231]. or improved therapies. However, when widespread Stable PDE5 silencing in the aggressive human breast malignancy is encountered, these cases are not responsive cancer cell line MDA-MB-231T lead to a reduction of cell to curative treatments. motility in vitro and of lung metastasis formations in an In several colon tumor cell lines (e.g. HT29, T84, experimental metastasis assay in vivo [232]. This well fits and HCT116), exisulind and analogs/derivatives were with our recent data showing that stable overexpression of able to inhibit the oncogenic activity of β-catenin through PDE5 in MCF-7 breast cancer cells significantly increased a direct suppression of its transcription or increased motility and invasion of all the stable PDE5- transfected proteosomal degradation, thereby promoting cell death clones tested compared to parental cells [7]. In addition [202, 235–238]. It was also reported that sulindac to the direct anti-cancer activities, it was demonstrated metabolites inhibit the mitogen-activated protein/ that PDE5 inhibitors may act as potential cancer extracellular signal-regulated kinase kinase (MEK/ chemopreventive agents, due to their ability to suppress ERK) signaling cascade in colorectal cancer cell lines 1-methyl-1-nitrosourea (MNU)-induced mammary at doses that induce apoptosis, as additional molecular carcinogenesis [233]. mechanisms by which Sulindac inhibits tumor cell growth In breast cancer clinical samples, increased [239, 240]. In addition, treatment of human colorectal PDE5 expression was verified by both RT-PCR and cancer cells with sildenafil resulted in cell proliferation immunohistochemistry analyses, and was correlated inhibition, cell cycle arrest and apoptosis accompanied with tumor grade stage and lymph node involvement by increased intracellular reactive oxidative specie levels [9, 234]. More recently, we demonstrated that PDE5 in vitro and caused the reduction of xenograft tumor was differentially expressed among breast cancer growth in nude mice [241]. Recently, combined inhibition molecular subtypes, with higher levels in HER2- of PDE5 and PDE10 by treatment with PDE isozyme- enriched and triple-negative subtypes compared to selective inhibitors, or by siRNA knockdown was shown the more favourable estrogen receptor (ER)-positive to suppresses β-catenin, and the levels of its downstream Luminal B- and the Luminal A subtypes [7]. Importantly, targets, thereby suppressing proliferation and inducing high PDE5 expression predict a worse prognosis for a apoptosis in colon tumor cells [242]. cohort of 1,988 patients at 8-year median follow-up [7]. In clinical studies, exisulind prevented colorectal Significant difference was also found between overall polyp formation in patients with familial adenomatous survival for ER-positive patients having high or low polyposis (FAP) over 24 months [243, 244]. Moreover, www.impactjournals.com/oncotarget 99188 Oncotarget it has been demonstrated that exisulind inhibited identifying this enzyme as a favourable prognostic marker azoxymethane-induced colon carcinogenesis in rats for GBM, which negatively affects cell invasiveness and [201] and sildenafil suppressed polyp formation and survival [253]. inflammation in mice treated with azoxymethane/dextrane sulfate sodium [245], highlighting the chemopreventive Thyroid cancer role of PDE5 inhibition [246]. Carcinoma of the thyroid is the most common Brain cancer malignancy of endocrine organs, representing 2.1% of the new cancer cases (about 230,000 among women Cancers of the brain and central nervous system and 70,000 among men in 2012) [254]. Over the last accounted for 256,000 new cases and 189,000 deaths in few decades, a steady increase of thyroid cancer has 2012, with the highest incidence and mortality rates in been appreciably observed in most areas of the world, more developed regions [2]. and if current trends are maintained, thyroid cancer may In both neuroblastoma N18TG2 and hybrid become the fourth most common cancer by 2030. More neuroblastoma-glioma NG108–15 cells, the presence and than 95% are well-differentiated papillary or follicular regulation of PDE5 mRNA during cell differentiation tumors that derive from follicular epithelial cells and was previously demonstrated [247]. In medulloblastoma can be effectively managed by surgical resection with or cells, PDE5 inhibitors interacted in a greater than without radioctive iodine ablation. A minority of thyroid additive fashion with vincristine/etoposide/cisplatin to cancers are medullary thyroid carcinomas that derive from cause cell death. PDE5 inhibitors promoted autophagy the neuroendocrine C cells of the thyroid or anaplastic and enhanced chemotherapy-induced DNA damage malignancies that are the rarest but the most lethal subtype in a nitric oxide synthase-dependent fashion [248]. [255]. Treatment for about two thirds of patients with Pharmacologic modulation of cGMP signaling is emerging progressive metastatic papillary and follicular thyroid as a novel approach for enhancing therapeutic agent cancers as well as for patients with less differentiated permeability across the blood-brain tumor barrier, thereby tumors is often of limited benefit, due to their inability to increasing delivery to brain tumors and metastases. Oral concentrate radioiodine or to the development of therapy administration of sildenafil and vardenafil selectively resistance [256, 257]. Thus, there is a pressing need for improved tumor capillary permeability in 9L gliosarcoma- innovative treatments in patients having high risk of bearing rats, without changes in normal brain capillaries disease-related death. [249]. Importantly, tumor-bearing rats treated with The role of cGMP levels and PDE5 in thyroid the chemotherapy agent, adriamycin, in combination cancer are still not well defined. Analysis of the mRNA with vardenafil exhibited a survival significantly longer expression of members of the 11 known families of PDEs than rats treated with adriamycin alone [249]. The has revealed the expression of PDE4, PDE5, PDE7 and combination of OSU-03012/sildenafil synergized with low PDE8 subtypes in normal thyroid tissues [258]. Previous concentrations of sorafenib to kill glioblastoma cells in studies have also reported the presence of PDE4 in toxic vitro and in vivo [250]. PDE5 inhibitors enhanced transport adenomas characterized by mutations in the TSH receptor and therapeutic efficacy of trastuzumab in hard-to-treat (TSH-R) gene [259]. In 2015, Sponziello et al. showed, for brain metastases from different primary tumors [251]. the first time, higher mRNA and protein expression levels Tadalafil can also enhance the treatment efficacy of the of PDE5 in a series of human papillary thyroid carcinomas chimeric anti-CD20 monoclonal antibody Rituximab by belonging to two independent cohorts compared to non- improving the microvascular permeability in intracranial tumor tissues [260]. Interestingly, tumors presenting brain lymphoma mice model [252]. In contrast to these BRAF V600E mutation, that is the most frequent genetic findings, it was shown that genetic and pharmacological alteration and also a marker of aggressiveness [261], inhibition of PDE5 activity strongly enhanced cell motility exhibited a marked upregulation of PDE5 respect to those and invasiveness in human glioblastoma T98G cells, without mutation. Increased PDE5 transcripts were also whereas PDE5 overexpression in PDE5-negative U87G associated with a reduction of the expression of TSH-R, cells significantly inhibited their invasive potential and thyroglobulin (Tg), thyroid peroxidase (TPO), sodium/ interfered with DNA damage repair and cell survival iodide symporter (NIS), important differentiation markers following irradiation [253]. implicated in intra-thyroidal iodine metabolism and Analysis of a cohort of 69 patients affected thyroid hormone synthesis. More recently, a second study by glioblastoma multiforme (GBM) who underwent reported higher intracellular cGMP levels and cGMP- chemotherapy and radiotherapy following surgical PDE activity in thyroid malignant (papillar and follicular) resection of the tumor revealed that PDE5 was strongly carcinomas than in controls and benign pathologies expressed in 50% of cancer cases [253]. Retrospective (i.e. benign struma, adenomatous hyperplasia, chronic analysis indicated that high PDE5 expression significantly thyroiditis, benign adenoma) [262]. However, the cGMP- correlated with increased overall survival of patients, PDE expression was elevated in papillary carcinomas www.impactjournals.com/oncotarget 99189 Oncotarget without lymph node involvement (N-) in respect to those in murine and human melanoma cells, suggesting that with lymph node invasion (N±), while cGMP levels possible skin adverse effects of PDE5 inhibitors should be displayed an inverse trend. These events may represent better considered [268]. an autophagic defence mechanism of the body against the Clinically, in a prospective cohort study, men cancer that is expanding and invading other tissues and who used sildenafil for ED had a statistically significant organs. Although these findings are promising, further elevated risk of developing melanoma, without affecting studies are needed to draw definitive conclusions. the risk of squamous or basal cell carcinomas, and this In papillary and anaplastic thyroid cancer cells correlation was maintained in the models controlling for in vitro, sildenafil and tadalafil determined a reduction the major host characteristics, such as age, body mass of proliferation and at lower doses, they were also able index, family history, sun exposure, and UV index in to reduce cellular migration [260]. The effects of PDE5 the state of residence [269]. A subsequent nationwide, inhibitors were stronger in the cancer cell lines carrying population-based, nested case-control study in Sweden, the BRAF mutation, suggesting that these tumors could including 4065 melanoma cases diagnosed from 2006 be a preferential subtype for the action of PDE5-targeted through 2012, showed that the use of PDE5 inhibitors drugs. A significant decrease of the drug dosages necessary was associated with a modest but statistically significant to achieve an anticancer effect was obtained with the increased risk of malignant melanoma, but the pattern encapsulation of these compounds within nanoliposomes of association (e.g. the lack of association with multiple [263], that may represent, if confirmed in vivo, a valuable filled prescriptions) raises questions about the causality of novel formulation for the treatment of thyroid carcinomas this relationship [270]. Later, a large UK-based primary and other types of cancers. care database, with 145,104 men who were prescribed a PDE5 inhibitor and 560,933 matched controls, was Melanoma examined, but the findings showed no evidence of a positive association between PDE5 inhibitor exposure Cutaneous melanoma accounted for almost 5% and melanoma risk after matching or adjusting for key of all new diagnosed cancer cases, with a reported potential confounders [271]. More recently, a meta- mortality of approximately 2%, making it the deadliest analysis of 5-population-based observational studies form of skin cancer. Although early detection carries an revealed an increased risk of malignant melanoma in excellent prognosis, with surgical excision often being users of PDE5 inhibitors for ED [272]. Although a large curative, the long-term survival rate for patients with number of patients and a long follow-up were included metastatic melanoma is only 5% [264]. The disease in this report, population selective bias, the lack of dose- derived from genetically altered epidermal melanocytes response analysis and in general the weakness inherent that arises because of complex interactions between in observational studies should be acknowledged. Thus, genetic alterations, such as RAS pathway mutations and collectively, the present findings are insufficient to alter environmental factors, especially exposure to UV radiation current clinical recommendation. [265]. The role of PDE5 on pathogenesis or progression of melanoma remains still an area of debate. Murata et al. Other cancers have shown PDE5 activity and expression in malignant melanoma cells, and reported an important function for A possible role of PDE5 inhibition has been this enzyme in regulating melanoma progression as two suggested also in the management of other cancers. PDE5 inhibitors inhibited cell growth [266]. However, Immunohistochemistry showed that PDE5 was the first mechanistic insights on the link between PDE5 overexpressed in human squamous and transitional and melanoma was suggested by Arozarena et al. in 2011 cell carcinomas compared with normal urothelium and [267]. Indeed, it was demonstrated that in melanoma accordingly, exisulind exhibited antineoplastic activity cells oncogenic BRAF, through the transcription factor in vivo in a model of rat urinary bladder tumorigenesis BRN2, was able to suppress PDE5A expression. PDE5 [8]. The addition of PDE5 inhibitors to multiple existing down-regulation, in turn, leads to enhanced cGMP treatment regimens, including doxorubicin, mitomycin levels, which induce an increase in cytosolic Ca2+, a C, gemcitabine, cisplatin and paclitaxel, significantly stimulation of actin-myosin contractility and a subsequent enhanced chemotherapy lethality by stimulating the increase in cell invasion in vitro and in vivo [267]. extrinsic apoptosis pathway via CD95 and by promoting Accordingly, immunohistochemistry analysis in a tissue autophagy through RIP-1 (receptor interacting protein microarray consisting of triplicate cores of 28 primary 1) in bladder and pancreatic cancer cell lines [156]. and 29 metastatic malignant melanoma cases revealed In human renal carcinoma cell lines, suppression of a statistically significant downregulation of PDE5A in PDE5 gene expression by PDE5 siRNA reduced cell metastatic tumors [267]. More recently, it was reported proliferation and induced apoptosis through cGMP-PKG that the growth-promoting cGMP signaling could be activation [273]. Sildenafil in combination with C-type potentiated pharmacologically by treatment with sildenafil natriuretic peptide synergistically inhibited proliferation www.impactjournals.com/oncotarget 99190 Oncotarget of rhabdomyosarcoma cells and suppressed tumor growth patient variables that may point toward the use of PDE5 in vivo [274]. Sildenafil and vardenafil were also able to inhibitors in general and each specific drug of this class, induce apoptosis in peripheral blood mononuclear cells providing antitumor therapy with reduced adverse effects. isolated from fourteen patients with chronic lymphocytic Certainly, the clarification of additional molecular leukemia through a caspase 3-dependent pathway processes of potential oncogenic function of PDE5 as [275]. Recently, it was shown that vardenafil potentiates well as further clinical trials including PDE5 inhibitors the killing effect of the green tea polyphenol (–) will help to facilitate better applications of PDE5 targeting epigallocatechin-O-3-gallate on leukaemia and multiple drugs in the area of cancer treatment. myeloma cells, without affecting normal cells [276, 277]. Interestingly, in a patient with end-stage relapsed/ CONFLICTS OF INTEREST refractory multiple myeloma, the addition of tadalafil reduced myeloid-derived suppressor cell function, that The authors declare they have no conflicts of interest. was associated to anti-myeloma immune responses and clinical benefit [278]. In 2015, a randomized, prospective, double blinded, placebo controlled, phase II clinical trial GRANT SUPPORT to determine the activity of PDE5 inhibitors on immune function in head and neck squamous cell carcinoma This work was supported by PROGRAMMA (HNSCC) patients was conducted [279]. Results “FUTURO IN RICERCA” Anno 2012 (#RBFR12FI27) showed that tadalafil can reverse tumor-specific immune and MFAG #16899 to I. Barone. suppression in these patients, with important therapeutic potential. REFERENCES

Concluding remarks 1. Torre LA, Bray F, Siegel RL, Ferlay J, Lortet-Tieulent J, Jemal A. Global cancer statistics, 2012. CA Cancer J Clin. Over the last decades, researchers have elucidated 2015; 65: 87–108. the roles that impairment of cGMP signaling pathway by 2. Torre LA, Siegel RL, Ward EM, Jemal A. Global cancer PDE5 activity inhibition plays in the regulation of tumor incidence and mortality rates and trends - an update. Cancer development, and progression. As a consequence, our Epidemiol Biomarkers Prev. 2016; 25:16–27. knowledge on the link between PDE5 inhibitors and cancer 3. Bourdeanu L, Liu EA. Systemic treatment for breast cancer: biology has expanded, holding great promise for future Chemotherapy and biotherapy agents. Semin Oncol Nurs. use of these agents in several cancers. Although evident 2015; 31:156–162. clinical controversial data come from patients affected by 4. Byron E, Pinder-Schenck M. Systemic and targeted therapies melanoma and glioblastoma multiforme, studies discussed for early-stage lung cancer. Cancer Control. 2014; 21:21–31. in this literature review show that PDE5 inhibition 5. Gomaa AI, Waked I. Recent advances in multidisciplinary could be associated with a decreased risk of cancer management of hepatocellular carcinoma. World J Hepatol. development and suppression of tumor progression in 2015; 7:673–687. several malignancies including those of the lung, prostate, breast and colorectum. PDE5 inhibitors may also provide 6. Shiota M, Eto M. Current status of primary an additional antitumor immune response in patients pharmacotherapy and future perspectives toward upfront affected by myeloma and head and neck squamous cell therapy for metastatic hormone-sensitive prostate cancer. carcinomas. In addition, a synergistic effect with current Int J Urol. 2016; 23:360–369. chemotherapeutic regimens and monoclonal antibodies 7. Catalano S, Campana A, Giordano C, Gyorffy B, Tarallo R, has been reported. However, this research suffered from Rinaldi A, Bruno G, Ferraro A, Romeo F, Lanzino M, Naro the weakness of the clinical studies conducted until now F, Bonofiglio D, Andò S, et al. Expression and function of that make difficult to draw a general conclusion. First, it phosphodiesterase type 5 in human breast cancer cell lines would be important to distinguish class effects of PDE5 and tissues: Implications for targeted therapy. Clin Cancer inhibitors versus effects unique to selective agents within Res. 2016; 22:2271–2282. the class, also in relation to non-specific inhibition of other 8. Piazza GA, Thompson WJ, Pamukcu R, Alila HW, PDEs as well as to potential off-target effects that can both Whitehead CM, Liu L, Fetter JR, Gresh WE Jr, Klein- positively and negatively influence the risk-benefit profile Szanto AJ, Farnell DR, Eto I Grubbs CJ. Exisulind, a of PDE5 inhibitors. Secondly, we will need information novel proapoptotic drug, inhibits rat urinary bladder concerning the optimal dosages of these molecules in the tumorigenesis. Cancer Res. 2001; 61:3961–3968. various applications, their monitoring, and the potential 9. Pusztai L, Zhen JH, Arun B, Rivera E, Whitehead C, interactions with other agents regularly used in each Thompson WJ, Nealy KM, Gibbs A, Symmans WF, Esteva patient population. Moreover, major clinical benefits will FJ, Booser D, Murray JL, Valero V, et al. Phase I and II come from more definitive specifications of individual study of exisulind in combination with capecitabine in www.impactjournals.com/oncotarget 99191 Oncotarget patients with metastatic breast cancer. J Clin Oncol. 2003; 23. Chan S, Yan C. PDE1 isozymes, key regulators of 21:3454–3461. pathological vascular remodeling. Curr Opin Pharmacol. 10. Whitehead CM, Earle KA, Fetter J, Xu S, Hartman T, 2011; 11:720–724. Chan DC, Zhao TL, Piazza G, Klein-Szanto AJ, Pamukcu 24. Medina AE. Therapeutic utility of phosphodiesterase type I R, Alila H, Bunn PA Jr, Thompson WJ. Exisulind-induced inhibitors in neurological conditions. Front Neurosci. 2011; 5:21. apoptosis in a non-small cell lung cancer orthotopic 25. Gomez L, Breitenbucher JG. PDE2 inhibition: Potential lung tumor model augments docetaxel treatment and for the treatment of cognitive disorders. Bioorg Med Chem contributes to increased survival. Mol Cancer Ther. 2003; Lett. 2013; 23:6522–6527. 2:479–488. 26. Mongillo M, Tocchetti CG, Terrin A, Lissandron V, 11. Savai R, Pullamsetti SS, Banat GA, Weissmann N, Ghofrani Cheung YF, Dostmann WR, Pozzan T, Kass DA, Paolocci HA, Grimminger F, Schermuly RT. Targeting cancer with N, Houslay MD, Zaccolo M. Compartmentalized phosphodiesterase inhibitors. Expert Opin Investig Drugs. phosphodiesterase-2 activity blunts beta-adrenergic cardiac 2010; 19:117–131. inotropy via an NO/cGMP-dependent pathway. Circ Res. 12. Barone I, Giordano C, Bonofiglio D, Catalano S, Andò S. 2006; 98:226–234. Phosphodiesterase type 5 as a candidate therapeutic target 27. Sadhu K, Hensley K, Florio VA, Wolda SL. Differential in cancers. Curr Pathobiol Rep. 2015; 3:193–201. expression of the cyclic GMP-stimulated phosphodiesterase 13. Azevedo MF, Faucz FR, Bimpaki E, Horvath A, Levy I, PDE2a in human venous and capillary endothelial cells. J de Alexandre RB, Ahmad F, Manganiello V, Stratakis CA. Histochem Cytochem. 1999; 47:895–906. Clinical and molecular genetics of the phosphodiesterases 28. Spiessberger B, Bernhard D, Herrmann S, Feil S, Werner C, (PDEs). Endocr Rev. 2014; 35:195–233. Luppa PB, Hofmann F. cGMP-dependent protein kinase II 14. Lefievre L, de Lamirande E, Gagnon C. Presence of and aldosterone secretion. FEBS J. 2009; 276:1007–1013. cyclic nucleotide phosphodiesterases PDE1A, existing as 29. Keravis T, Lugnier C. Cyclic nucleotide phosphodiesterase a stable complex with calmodulin, and PDE3a in human (PDE) isozymes as targets of the intracellular signalling spermatozoa. Biol Reprod. 2002; 67:423–430. network: Benefits of PDE inhibitors in various diseases 15. Kanda N, Watanabe S. Regulatory roles of adenylate and perspectives for future therapeutic developments. Br J cyclase and cyclic nucleotide phosphodiesterases 1 and 4 Pharmacol. 2012; 165:1288–1305. in interleukin-13 production by activated human T cells. 30. Degerman E, Belfrage P, Manganiello VC. Structure, Biochem Pharmacol. 2001; 62:495–507. localization, and regulation of cGMP-inhibited 16. Deng C, Wang D, Bugaj-Gaweda B, De Vivo M. Assays for phosphodiesterase (PDE3). J Biol Chem. 1997; 272:6823–6826. cyclic nucleotide-specific phosphodiesterases (PDEs) in the 31. Murata T, Shimizu K, Hiramoto K, Tagawa T. central nervous system (PDE1, PDE2, PDE4, and PDE10). Phosphodiesterase 3 (PDE3): Structure, localization and Curr Protoc Neurosci. 2007; Chapter 7:Unit 7 21. function. Cardiovasc Hematol Agents Med Chem. 2009; 17. Nagel DJ, Aizawa T, Jeon KI, Liu W, Mohan A, Wei 7:206–211. H, Miano JM, Florio VA, Gao P, Korshunov VA, 32. Beca S, Ahmad F, Shen W, Liu J, Makary S, Polidovitch Berk BC, Yan C. Role of nuclear Ca2+/calmodulin- N, Sun J, Hockman S, Chung YW, Movsesian M, Murphy stimulated phosphodiesterase 1A in vascular smooth muscle E, Manganiello V, Backx PH. Phosphodiesterase type 3A cell growth and survival. Circ Res. 2006; 98:777–784. regulates basal myocardial contractility through interacting 18. Rybalkin SD, Rybalkina I, Beavo JA, Bornfeldt KE. Cyclic with sarcoplasmic reticulum calcium atpase type 2A nucleotide phosphodiesterase 1c promotes human arterial signaling complexes in mouse heart. Circ Res. 2013; smooth muscle cell proliferation. Circ Res. 2002; 90:151– 112:289–297. 157. 33. Begum N, Shen W, Manganiello V. Role of PDE3a in 19. Keravis T, Lugnier C. Cyclic nucleotide phosphodiesterases regulation of cell cycle progression in mouse vascular (PDE) and peptide motifs. Curr Pharm Des. 2010; 16:1114– smooth muscle cells and oocytes: Implications in 1125. cardiovascular diseases and infertility. Curr Opin 20. Dunkern TR, Hatzelmann A. Characterization of inhibitors Pharmacol. 2011; 11:725–729. of phosphodiesterase 1c on a human cellular system. FEBS 34. Sallstrom J, Jensen BL, Skott O, Gao X, Persson AE. J. 2007; 274:4812–4824. Neuronal nitric oxide synthase supports renin release during 21. Reneerkens OA, Rutten K, Steinbusch HW, Blokland sodium restriction through inhibition of phosphodiesterase A, Prickaerts J. Selective phosphodiesterase inhibitors: 3. Am J Hypertens. 2010; 23:1241–1246. a promising target for cognition enhancement. 35. Uckert S, Oelke M. Phosphodiesterase (PDE) inhibitors in Psychopharmacology (Berl). 2009; 202:419–443. the treatment of lower urinary tract dysfunction. Br J Clin 22. Essayan DM. Cyclic nucleotide phosphodiesterase (PDE) Pharmacol. 2011; 72:197–204. inhibitors and immunomodulation. Biochem Pharmacol. 36. Ochiai K, Takita S, Eiraku T, Kojima A, Iwase K, Kishi 1999; 57:965–973. T, Fukuchi K, Yasue T, Adams DR, Allcock RW, Jiang www.impactjournals.com/oncotarget 99192 Oncotarget Z, Kohno Y. Phosphodiesterase inhibitors. Part 3: 49. Kulkarni SK, Patil CS. Phosphodiesterase 5 enzyme and its Design, synthesis and structure-activity relationships of inhibitors: Update on pharmacological and therapeutical aspects. dual PDE3/4-inhibitory fused bicyclic heteroaromatic- Methods Find Exp Clin Pharmacol. 2004; 26:789–799. dihydropyridazinones with anti-inflammatory and 50. d’Esterre CD, Lee TY. Effect of dipyridamole during acute bronchodilatory activity. Bioorg Med Chem. 2012; stroke: Exploring antithrombosis and neuroprotective 20:1644–1658. benefits. Ann N Y Acad Sci. 2010; 1207:71–75. 37. Sakakibara H, Conti M, Weiner RI. Role of 51. Forrest CM, Stoy N, Stone TW, Harman G, Mackay phosphodiesterases in the regulation of gonadotropin- GM, Oxford L, Darlington LG. Adenosine and cytokine releasing hormone secretion in GT1 cells. levels following treatment of rheumatoid arthritis with Neuroendocrinology. 1998; 68:365–373. dipyridamole. Rheumatol Int. 2006; 27:11–17. 38. Diamant Z, Spina D. PDE4-inhibitors: A novel, targeted 52. Spano D, Marshall JC, Marino N, De Martino D, Romano therapy for obstructive airways disease. Pulm Pharmacol A, Scoppettuolo MN, Bello AM, Di Dato V, Navas L, De Ther. 2011; 24:353–360. Vita G, Medaglia C, Steeg PS, Zollo M. Dipyridamole 39. Jin SL, Ding SL, Lin SC. Phosphodiesterase 4 and its prevents triple-negative breast-cancer progression. Clin Exp inhibitors in inflammatory diseases. Chang Gung Med J. Metastasis. 2013; 30:47–68. 2012; 35:197–210. 53. Puzzo D, Sapienza S, Arancio O, Palmeri A. Role of 40. Vang AG, Basole C, Dong H, Nguyen RK, Housley W, phosphodiesterase 5 in synaptic plasticity and memory. Guernsey L, Adami AJ, Thrall RS, Clark RB, Epstein PM, Neuropsychiatr Dis Treat. 2008; 4:371–387. Brocke S. Differential expression and function of PDE8 and 54. Zhu B, Strada SJ. The novel functions of cGMP-specific PDE4 in effector t cells: Implications for PDE8 as a drug phosphodiesterase 5 and its inhibitors in carcinoma cells target in inflammation. Front Pharmacol. 2016; 7:259. and pulmonary/cardiovascular vessels. Curr Top Med 41. Richter W, Menniti FS, Zhang HT, Conti M. PDE4 as a Chem. 2007; 7:437–454. target for cognition enhancement. Expert Opin Ther Targets. 55. Kukreja RC, Salloum FN, Das A, Koka S, Ockaili RA, Xi 2013; 17:1011–1027. L. Emerging new uses of phosphodiesterase-5 inhibitors 42. Richter W, Xie M, Scheitrum C, Krall J, Movsesian MA, Conti in cardiovascular diseases. Exp Clin Cardiol. 2011; M. Conserved expression and functions of PDE4 in rodent and 16:e30–35. human heart. Basic Res Cardiol. 2011; 106:249–262. 56. Das A, Durrant D, Salloum FN, Xi L, Kukreja RC. PDE5 43. Fujita M, Hines CS, Zoghbi SS, Mallinger AG, Dickstein inhibitors as therapeutics for heart disease, diabetes and LP, Liow JS, Zhang Y, Pike VW, Drevets WC, Innis RB, cancer. Pharmacol Ther. 2015; 147:12–21. Zarate CA Jr. Downregulation of brain phosphodiesterase 57. Guazzi M, Vicenzi M, Arena R, Guazzi MD. PDE5 type IV measured with 11c-(r)-rolipram positron emission inhibition with sildenafil improves left ventricular diastolic tomography in major depressive disorder. Biol Psychiatry. function, cardiac geometry, and clinical status in patients 2012; 72:548–554. with stable systolic heart failure: Results of a 1-year, 44. Houslay MD. The long and short of vascular smooth muscle prospective, randomized, placebo-controlled study. Circ phosphodiesterase-4 as a putative therapeutic target. Mol Heart Fail. 2011; 4:8–17. Pharmacol. 2005; 68:563–567. 58. Kolandaivelu S, Chang B, Ramamurthy V. Rod 45. McKenna SD, Pietropaolo M, Tos EG, Clark A, Fischer D, phosphodiesterase-6 (PDE6) catalytic subunits restore cone Kagan D, Bao B, Chedrese PJ, Palmer S. Pharmacological function in a mouse model lacking cone PDE6 catalytic inhibition of phosphodiesterase 4 triggers ovulation in subunit. J Biol Chem. 2011; 286:33252–33259. follicle-stimulating hormone-primed rats. Endocrinology. 59. Cote RH. Characteristics of photoreceptor PDE (PDE6): 2005; 146:208–214. Similarities and differences to PDE5. Int J Impot Res. 2004; 46. Page CP, Spina D. Phosphodiesterase inhibitors in the 16:S28–33. treatment of inflammatory diseases. Handb Exp Pharmacol. 60. Muradov KG, Granovsky AE, Artemyev NO. Mutation in 2011; 391–414. rod PDE6 linked to congenital stationary night blindness 47. Santos-Silva AJ, Cairrao E, Morgado M, Alvarez E, Verde impairs the enzyme inhibition by its gamma-subunit. I. PDE4 and PDE5 regulate cyclic nucleotides relaxing Biochemistry. 2003; 42:3305–3310. effects in human umbilical arteries. Eur J Pharmacol. 2008; 61. Christiansen JR, Ramamurthy V. Greasing the protein 582:102–109. biosynthesis machinery of photoreceptor neurons: Role for 48. Reneerkens OA, Rutten K, Akkerman S, Blokland A, postprenylation processing of proteins. Cell Logist. 2012; Shaffer CL, Menniti FS, Steinbusch HW, Prickaerts J. 2:15–19. Phosphodiesterase type 5 (PDE5) inhibition improves 62. Dong H, Osmanova V, Epstein PM, Brocke S. object recognition memory: Indications for central and Phosphodiesterase 8 (PDE8) regulates chemotaxis of peripheral mechanisms. Neurobiol Learn Mem. 2012; activated lymphocytes. Biochem Biophys Res Commun. 97:370–379. 2006; 345:713–719. www.impactjournals.com/oncotarget 99193 Oncotarget 63. Vasta V, Shimizu-Albergine M, Beavo JA. Modulation GS, Thomson PA, Hill EV, Brandon NJ, et al. DISC1 and of leydig cell function by cyclic nucleotide PDE4B are interacting genetic factors in schizophrenia that phosphodiesterase 8A. Proc Natl Acad Sci U S A. 2006; regulate cAMP signaling. Science. 2005; 310:1187–1191. 103:19925–19930. 78. Conti M, Beavo J. Biochemistry and physiology of cyclic 64. Arnaud-Lopez L, Usala G, Ceresini G, Mitchell BD, Pilia nucleotide phosphodiesterases: Essential components in MG, Piras MG, Sestu N, Maschio A, Busonero F, Albai G, cyclic nucleotide signaling. Annu Rev Biochem. 2007; Dei M, Lai S, Mulas A, et al. Phosphodiesterase 8B gene 76:481–511. variants are associated with serum TSH levels and thyroid 79. Horvath A, Mericq V, Stratakis CA. Mutation in PDE8B, function. Am J Hum Genet. 2008; 82:1270–1280. a cyclic AMP-specific phosphodiesterase in adrenal 65. Su T, Zhang T, Xie S, Yan J, Wu Y, Li X, Huang L, Luo HB. hyperplasia. N Engl J Med. 2008; 358:750–752. Discovery of novel PDE9 inhibitors capable of inhibiting 80. Yanaka N, Kotera J, Ohtsuka A, Akatsuka H, Imai Aβ aggregation as potential candidates for the treatment of Y, Michibata H, Fujishige K, Kawai E, Takebayashi Alzheimer’s disease. Sci Rep. 2016; 6:21826. S, Okumura K, Omori K. Expression, structure and 66. Andreeva SG, Dikkes P, Epstein PM, Rosenberg PA. chromosomal localization of the human cGMP-binding Expression of cGMP-specific phosphodiesterase 9A mRNA cGMP-specific phosphodiesterase PDE5A gene. Eur J in the rat brain. J Neurosci. 2001; 21:9068–9076. Biochem. 1998; 255:391–399. 67. Reneerkens OA, Rutten K, Bollen E, Hage T, Blokland A, 81. Lin CS. Tissue expression, distribution, and regulation of Steinbusch HW, Prickaerts J. Inhibition of phoshodiesterase PDE5. Int J Impot Res. 2004; 16:S8-S10. type 2 or type 10 reverses object memory deficits induced by 82. Lin CS, Lau A, Tu R, Lue TF. Identification of three alternative scopolamine or MK-801. Behav Brain Res. 2013; 236:16–22. first exons and an intronic promoter of human PDE5A gene. 68. Jager R, Russwurm C, Schwede F, Genieser HG, Koesling Biochem Biophys Res Commun. 2000; 268:596–602. D, Russwurm M. Activation of PDE10 and PDE11 83. Lin CS, Chow S, Lau A, Tu R, Lue TF. Identification and phosphodiesterases. J Biol Chem. 2012; 287:1210–1219. regulation of human PDE5A gene promoter. Biochem 69. Horvath A, Korde L, Greene MH, Libe R, Osorio P, Faucz Biophys Res Commun. 2001; 280:684–692. FR, Raffin-Sanson ML, Tsang KM, Drori-Herishanu 84. Lin CS, Chow S, Lau A, Tu R, Lue TF. Regulation of L, Patronas Y, Remmers EF, Nikita ME, Moran J, et al. human PDE5A2 intronic promoter by cAMP and cGMP: Functional phosphodiesterase 11A mutations may modify Identification of a critical sp1-binding site. Biochem the risk of familial and bilateral testicular germ cell tumors. Biophys Res Commun. 2001; 280:693–699. Cancer Res. 2009; 69:5301–5306. 85. Lin CS, Chow S, Lau A, Tu R, Lue TF. Human PDE5A gene 70. Faucz FR, Horvath A, Rothenbuhler A, Almeida MQ, Libe encodes three PDE5 isoforms from two alternate promoters. R, Raffin-Sanson ML, Bertherat J, Carraro DM, Soares FA, Int J Impot Res. 2002; 14:15–24. Molina Gde C, Campos AH, Alexandre RB, Bendhack ML, 86. Aravind L, Ponting CP. The gaf domain: An evolutionary et al. Phosphodiesterase 11A (PDE11A) genetic variants link between diverse phototransducing proteins. Trends may increase susceptibility to prostatic cancer. J Clin Biochem Sci. 1997; 22:458–459. Endocrinol Metab. 2011; 96:E135–140. 87. Corbin JD, Turko IV, Beasley A, Francis SH. 71. Pomara G, Morelli G. Inhibition of phosphodiesterase 11 Phosphorylation of phosphodiesterase-5 by cyclic (PDE11) impacts on sperm quality. Int J Impot Res. 2005; nucleotide-dependent protein kinase alters its catalytic and 17:385–386; author reply 387. allosteric cGMP-binding activities. Eur J Biochem. 2000; 72. Seftel AD. Phosphodiesterase 11 (PDE11) regulation of 267:2760–2767. spermatozoa physiology. J Urol. 2005; 174:1043–1044. 88. Zoraghi R, Bessay EP, Corbin JD, Francis SH. Structural 73. Ke H, Wang H, Ye M. Structural insight into the substrate and functional features in human PDE5a1 regulatory domain specificity of phosphodiesterases. Handb Exp Pharmacol. that provide for allosteric cGMP binding, dimerization, and 2011; 121–134. regulation. J Biol Chem. 2005; 280:12051–12063. 74. Francis SH, Turko IV, Corbin JD. Cyclic nucleotide 89. Turko IV, Francis SH, Corbin JD. Binding of cGMP phosphodiesterases: Relating structure and function. Prog to both allosteric sites of cGMP-binding cGMP- Nucleic Acid Res Mol Biol. 2001; 65:1–52. specific phosphodiesterase (PDE5) is required for its 75. Bender AT, Beavo JA. Cyclic nucleotide phosphorylation. Biochem J. 1998; 329:505–510. phosphodiesterases: Molecular regulation to clinical use. 90. Francis SH, Bessay EP, Kotera J, Grimes KA, Liu L, Pharmacol Rev. 2006; 58:488–520. Thompson WJ, Corbin JD. Phosphorylation of isolated 76. Francis SH, Blount MA, Corbin JD. Mammalian cyclic human phosphodiesterase-5 regulatory domain induces nucleotide phosphodiesterases: Molecular mechanisms and an apparent conformational change and increases cGMP physiological functions. Physiol Rev. 2011; 91:651–690. binding affinity. J Biol Chem. 2002; 277:47581–47587. 77. Millar JK, Pickard BS, Mackie S, James R, Christie S, 91. Omori K, Kotera J. Overview of PDEs and their regulation. Buchanan SR, Malloy MP, Chubb JE, Huston E, Baillie Circ Res. 2007; 100:309–327. www.impactjournals.com/oncotarget 99194 Oncotarget 92. Kass DA, Takimoto E, Nagayama T, Champion HC. 105. Nagendran J, Archer SL, Soliman D, Gurtu V, Moudgil Phosphodiesterase regulation of nitric oxide signaling. R, Haromy A, St Aubin C, Webster L, Rebeyka IM, Ross Cardiovasc Res. 2007; 75:303–314. DB, Light PE, Dyck JR, Michelakis ED. Phosphodiesterase 93. Zhang M, Koitabashi N, Nagayama T, Rambaran R, Feng N, type 5 is highly expressed in the hypertrophied human right Takimoto E, Koenke T, O’Rourke B, Champion HC, Crow ventricle, and acute inhibition of phosphodiesterase type 5 MT, Kass DA. Expression, activity, and pro-hypertrophic improves contractility. Circulation. 2007; 116:238–248. effects of PDE5A in cardiac myocytes. Cell Signal. 2008; 106. Takimoto E, Champion HC, Li M, Belardi D, Ren S, 20:2231–2236. Rodriguez ER, Bedja D, Gabrielson KL, Wang Y, Kass 94. Castro LR, Schittl J, Fischmeister R. Feedback control DA. Chronic inhibition of cyclic GMP phosphodiesterase through cGMP-dependent protein kinase contributes to 5A prevents and reverses cardiac hypertrophy. Nat Med. differential regulation and compartmentation of cGMP in 2005; 11:214–222. rat cardiac myocytes. Circ Res. 2010; 107:1232–1240. 107. Dunkern TR, Hatzelmann A. The effect of sildenafil 95. Zhao CY, Greenstein JL, Winslow RL. Roles of on human platelet secretory function is controlled by a phosphodiesterases in the regulation of the cardiac cyclic complex interplay between phosphodiesterases 2, 3 and 5. nucleotide cross-talk signaling network. J Mol Cell Cardiol. Cell Signal. 2005; 17:331–339. 2016; 91:215–227. 108. Prickaerts J, Sik A, van Staveren WC, Koopmans G, 96. Mullershausen F, Friebe A, Feil R, Thompson WJ, Hofmann Steinbusch HW, van der Staay FJ, de Vente J, Blokland A. F, Koesling D. Direct activation of PDE5 by cGMP: Long- Phosphodiesterase type 5 inhibition improves early memory term effects within NO/cGMP signaling. J Cell Biol. 2003; consolidation of object information. Neurochem Int. 2004; 160:719–727. 45:915–928. 97. Lochhead A, Nekrasova E, Arshavsky VY, Pyne NJ. The 109. Lugnier C, Schoeffter P, Le Bec A, Strouthou E, Stoclet JC. regulation of the cGMP-binding cGMP phosphodiesterase Selective inhibition of cyclic nucleotide phosphodiesterases by proteins that are immunologically related to gamma of human, bovine and rat aorta. Biochem Pharmacol. 1986; subunit of the photoreceptor cGMP phosphodiesterase. J 35:1743–1751. Biol Chem. 1997; 272:18397–18403. 110. Schwartz BG, Kloner RA. Drug interactions with 98. Campolo F, Zevini A, Cardarelli S, Monaco L, Barbagallo F, phosphodiesterase-5 inhibitors used for the treatment Pellegrini M, Cornacchione M, Di Grazia A, De Arcangelis of erectile dysfunction or pulmonary hypertension. V, Gianfrilli D, Giorgi M, Lenzi A, Isidori AM, et al. Circulation. 2010; 122:88–95. Identification of murine phosphodiesterase 5a isoforms and 111. Gresser U, Gleiter CH. Erectile dysfunction: Comparison of their functional characterization in hl-1 cardiac cell line. J efficacy and side effects of the PDE-5 inhibitors sildenafil, Cell Physiol. 2018; 233:325–337. vardenafil and tadalafil - review of the literature. Eur J Med 99. Rehmann H, Wittinghofer A, Bos JL. Capturing cyclic Res. 2002; 7:435–446. nucleotides in action: Snapshots from crystallographic 112. Daugan A, Grondin P, Ruault C, Le Monnier de studies. Nat Rev Mol Cell Biol. 2007; 8:63–73. Gouville AC, Coste H, Linget JM, Kirilovsky J, Hyafil 100. Hofmann F, Bernhard D, Lukowski R, Weinmeister P. F, Labaudiniere R. The discovery of tadalafil: A novel cGMP regulated protein kinases (CGK). Handb Exp and highly selective PDE5 inhibitor. 2: 2, 3, 6, 7, 12, Pharmacol. 2009; 137–162. 12a-hexahydropyrazino[1’, 2’:1, 6]pyrido[3,4-b]indole-1,4- 101. Francis SH, Busch JL, Corbin JD, Sibley D. cGMP- dione analogues. J Med Chem. 2003; 46:4533–4542. dependent protein kinases and cGMP phosphodiesterases 113. Weeks JL, Zoraghi R, Beasley A, Sekhar KR, Francis in nitric oxide and cGMP action. Pharmacol Rev. 2010; SH, Corbin JD. High biochemical selectivity of tadalafil, 62:525–563. sildenafil and vardenafil for human phosphodiesterase 102. Hood J, Granger HJ. Protein kinase g mediates vascular 5A1 (PDE5) over PDE11A4 suggests the absence of endothelial growth factor-induced RAF-1 activation and PDE11A4 cross-reaction in patients. Int J Impot Res. proliferation in human endothelial cells. J Biol Chem. 1998; 2005; 17:5–9. 273:23504–23508. 114. Porst H, Padma-Nathan H, Giuliano F, Anglin G, Varanese 103. Smolenski A, Poller W, Walter U, Lohmann SM. Regulation L, Rosen R. Efficacy of tadalafil for the treatment of erectile of human endothelial cell focal adhesion sites and migration dysfunction at 24 and 36 hours after dosing: A randomized by cGMP-dependent protein kinase i. J Biol Chem. 2000; controlled trial. Urology. 2003; 62:121–125; discussion 275:25723–25732. 125–126. 104. Kook H, Itoh H, Choi BS, Sawada N, Doi K, Hwang 115. Kotera J, Mochida H, Inoue H, Noto T, Fujishige K, Sasaki TJ, Kim KK, Arai H, Baik YH, Nakao K. Physiological T, Kobayashi T, Kojima K, Yee S, Yamada Y, Kikkawa concentration of atrial natriuretic peptide induces K, Omori K. Avanafil, a potent and highly selective endothelial regeneration in vitro. Am J Physiol Heart Circ phosphodiesterase-5 inhibitor for erectile dysfunction. J Physiol. 2003; 284:H1388–1397. Urol. 2012; 188:668–674. www.impactjournals.com/oncotarget 99195 Oncotarget 116. Kim BH, Lim HS, Chung JY, Kim JR, Lim KS, Sohn Tamsulosin vs. Tamsulosin plus tadalafil in the treatment of DR, Cho JY, Yu KS, Shin SG, Paick JS, Jang IJ. Safety, LUTS/BPH. Pilot study. J Sex Med. 2008; 5:2170–2178. tolerability and pharmacokinetics of udenafil, a novel PDE- 129. Roehrborn CG, Kaminetsky JC, Auerbach SM, Montelongo 5 inhibitor, in healthy young korean subjects. Br J Clin RM, Elion-Mboussa A, Viktrup L. Changes in peak Pharmacol. 2008; 65:848–854. urinary flow and voiding efficiency in men with signs and 117. Lee HS, Park EJ, Ji HY, Kim SY, Im GJ, Lee SM, Jang symptoms of benign prostatic hyperplasia during once daily IJ. Identification of cytochrome p450 enzymes responsible tadalafil treatment. BJU Int. 2010; 105:502–507. for n-dealkylation of a new oral erectogenic, mirodenafil. 130. Cellek S, Cameron NE, Cotter MA, Fry CH, Ilo D. Xenobiotica. 2008; 38:21–33. Microvascular dysfunction and efficacy of PDE5 inhibitors 118. Toque HA, Teixeira CE, Lorenzetti R, Okuyama CE, in LUTS/BPH. Nat Rev Urol. 2014; 11:231–241. Antunes E, De Nucci G. Pharmacological characterization 131. Gonzalez-Cadavid NF, Rajfer J. Treatment of peyronie’s of a novel phosphodiesterase type 5 (PDE5) inhibitor disease with PDE5 inhibitors: An antifibrotic strategy. Nat lodenafil carbonate on human and rabbit corpus Rev Urol. 2010; 7:215–221. cavernosum. Eur J Pharmacol. 2008; 591:189–195. 132. Backhaus BO, Muller SC, Albers P. Corporoplasty for 119. Toque HA, Teixeira CE, Priviero FB, Morganti RP, advanced peyronie’s disease using venous and/or dermis Antunes E, De Nucci G. Vardenafil, but not sildenafil or patch grafting: New surgical technique and long-term tadalafil, has calcium-channel blocking activity in rabbit patient satisfaction. J Urol. 2003; 169:981–984. isolated pulmonary artery and human washed platelets. Br J 133. Goyal NK, Kumar A, Das SK, Pandey AK, Sharma GK, Pharmacol. 2008; 154:787–796. Trivedi S, Dwivedi US, Singh PB. Experience with plaque 120. Shi Z, Tiwari AK, Shukla S, Robey RW, Singh S, Kim IW, excision and dermal grafting in the surgical treatment of Bates SE, Peng X, Abraham I, Ambudkar SV, Talele TT, Peyronie’s disease. Singapore Med J. 2008; 49:805–808. Fu LW, Chen ZS. Sildenafil reverses ABCB1- and ABCG2- 134. Schwarzer JU, Muhlen B, Schukai O. Penile corporoplasty mediated chemotherapeutic drug resistance. Cancer Res. using tunica albuginea free graft from proximal corpus 2011; 71:3029–3041. cavernosum: A new technique for treatment of penile 121. Shi Z, Tiwari AK, Patel AS, Fu LW, Chen ZS. Roles of curvature in Peyronie’s disease. Eur Urol. 2003; 44:720– sildenafil in enhancing drug sensitivity in cancer. Cancer 723. Res. 2011; 71:3735–3738. 135. Levey HR, Segal RL, Bivalacqua TJ. Management of 122. Henrie AM, Nawarskas JJ, Anderson JR. Clinical utility of priapism: An update for clinicians. Ther Adv Urol. 2014; tadalafil in the treatment of pulmonary arterial hypertension: 6:230–244. An evidence-based review. Core Evid. 2015; 10:99–109. 136. Burnett AL, Bivalacqua TJ, Champion HC, Musicki B. 123. Butrous G. The role of phosphodiesterase inhibitors in the Feasibility of the use of phosphodiesterase type 5 inhibitors management of pulmonary vascular diseases. Glob Cardiol in a pharmacologic prevention program for recurrent Sci Pract. 2014; 2014:257–290. priapism. J Sex Med. 2006; 3:1077–1084. 124. Kloner RA, Comstock G, Levine LA, Tiger S, 137. Rajfer J, Gore JL, Kaufman J, Gonzalez-Cadavid N. Case Stecher VJ. Investigational noncardiovascular uses of report: Avoidance of palpable corporal fibrosis due to phosphodiesterase-5 inhibitors. Expert Opin Pharmacother. priapism with upregulators of nitric oxide. J Sex Med. 2006; 2011; 12:2297–2313. 3:173–176. 125. Kaplan SA, Gonzalez RR, Te AE. Combination of alfuzosin 138. McMahon CG, McMahon CN, Leow LJ, Winestock CG. and sildenafil is superior to monotherapy in treating lower Efficacy of type-5 phosphodiesterase inhibitors in the drug urinary tract symptoms and erectile dysfunction. Eur Urol. treatment of premature ejaculation: A systematic review. 2007; 51:1717–1723. BJU Int. 2006; 98:259–272. 126. Liguori G, Trombetta C, De Giorgi G, Pomara G, Maio G, 139. Mattos RM, Marmo Lucon A, Srougi M. Tadalafil Vecchio D, Ocello G, Ollandini G, Bucci S, Belgrano E. and fluoxetine in premature ejaculation: Prospective, Efficacy and safety of combined oral therapy with tadalafil randomized, double-blind, placebo-controlled study. Urol and alfuzosin: An integrated approach to the management Int. 2008; 80:162–165. of patients with lower urinary tract symptoms and erectile 140. Hosseini MM, Yarmohammadi H. Effect of fluoxetine dysfunction. Preliminary report. J Sex Med. 2009; 6:544–552. alone and in combination with sildenafil in patients with 127. Tuncel A, Nalcacioglu V, Ener K, Aslan Y, Aydin O, Atan premature ejaculation. Urol Int. 2007; 79:28–32. A. Sildenafil citrate and Tamsulosin combination is not 141. Dimitriadis F, Tsambalas S, Tsounapi P, Kawamura H, superior to monotherapy in treating lower urinary tract Vlachopoulou E, Haliasos N, Gratsias S, Watanabe T, Saito symptoms and erectile dysfunction. World J Urol. 2010; M, Miyagawa I, Sofikitis N. Effects of phosphodiesterase-5 28:17–22. inhibitors on Leydig cell secretory function in 128. Bechara A, Romano S, Casabe A, Haime S, Dedola P, oligoasthenospermic infertile men: A randomized trial. BJU Hernandez C, Rey H. Comparative efficacy assessment of Int. 2010; 106:1181–1185. www.impactjournals.com/oncotarget 99196 Oncotarget 142. Glenn DR, McVicar CM, McClure N, Lewis SE. Sildenafil attenuates doxorubicin-induced cardiomyopathy without citrate improves sperm motility but causes a premature interfering with chemotherapeutic effect. J Pharmacol Exp acrosome reaction in vitro. Fertil Steril. 2007; 87:1064– Ther. 2010; 334:1023–1030. 1070. 155. Fisher PW, Salloum F, Das A, Hyder H, Kukreja RC. 143. Francis SH. Phosphodiesterase 11 (PDE11): Is it a player in Phosphodiesterase-5 inhibition with sildenafil attenuates human testicular function? Int J Impot Res. 2005; 17:467– cardiomyocyte apoptosis and left ventricular dysfunction in 468. a chronic model of doxorubicin cardiotoxicity. Circulation. 144. Pomara G, Morelli G, Canale D, Turchi P, Caglieresi C, 2005; 111:1601–1610. Moschini C, Liguori G, Selli C, Macchia E, Martino E, 156. Booth L, Roberts JL, Cruickshanks N, Conley A, Durrant Francesca F. Alterations in sperm motility after acute oral DE, Das A, Fisher PB, Kukreja RC, Grant S, Poklepovic administration of sildenafil or tadalafil in young, infertile A, Dent P. Phosphodiesterase 5 inhibitors enhance men. Fertil Steril. 2007; 88:860–865. chemotherapy killing in gastrointestinal/genitourinary 145. Mostafa T. Tadalafil as anin vitro sperm motility stimulant. cancer cells. Mol Pharmacol. 2014; 85:408–419. Andrologia. 2007; 39:12–15. 157. Lee KW, Jeong JY, Lim BJ, Chang YK, Lee SJ, Na KR, 146. Zhang L, Zhang Z, Zhang RL, Cui Y, LaPointe MC, Shin YT, Choi DE. Sildenafil attenuates renal injury in an Silver B, Chopp M. Tadalafil, a long-acting type 5 experimental model of rat cisplatin-induced nephrotoxicity. phosphodiesterase isoenzyme inhibitor, improves Toxicology. 2009; 257:137–143. neurological functional recovery in a rat model of embolic 158. Medeiros JV, Gadelha GG, Lima SJ, Garcia JA, Soares stroke. Brain Res. 2006; 1118:192–198. PM, Santos AA, Brito GA, Ribeiro RA, Souza MH. Role 147. Zhang RL, Zhang Z, Zhang L, Wang Y, Zhang C, Chopp of the NO/cGMP/K(ATP) pathway in the protective effects M. Delayed treatment with sildenafil enhances neurogenesis of sildenafil against ethanol-induced gastric damage in rats. and improves functional recovery in aged rats after focal Br J Pharmacol. 2008; 153:721–727. cerebral ischemia. J Neurosci Res. 2006; 83:1213–1219. 159. Kato N, Mashita Y, Kato S, Mitsufuji S, Yoshikawa T, 148. Ding G, Jiang Q, Li L, Zhang L, Zhang ZG, Ledbetter Takeuchi K. Sildenafil, an inhibitor of phosphodiesterase KA, Panda S, Davarani SP, Athiraman H, Li Q, Ewing JR, subtype 5, prevents indomethacin-induced small-intestinal Chopp M. Magnetic resonance imaging investigation of ulceration in rats via a NO/cGMP-dependent mechanism. axonal remodeling and angiogenesis after embolic stroke Dig Dis Sci. 2009; 54:2346–2356. in sildenafil-treated rats. J Cereb Blood Flow Metab. 2008; 160. Soydan G, Sokmensuer C, Kilinc K, Tuncer M. The effects 28:1440–1448. of sildenafil on the functional and structural changes of 149. Silver B, McCarthy S, Lu M, Mitsias P, Russman AN, ileum induced by intestinal ischemia-reperfusion in rats. Katramados A, Morris DC, Lewandowski CA, Chopp M. Eur J Pharmacol. 2009; 610:87–92. Sildenafil treatment of subacute ischemic stroke: A safety 161. Gertner E. Treatment with sildenafil for the healing study at 25-mg daily for 2 weeks. J Stroke Cerebrovasc Dis. of refractory skin ulcerations in the antiphospholipid 2009; 18:381–383. syndrome. Lupus. 2003; 12:133–135. 150. Cuadrado-Tejedor M, Hervias I, Ricobaraza A, Puerta E, 162. Colglazier CL, Sutej PG, O’Rourke KS. Severe refractory Perez-Roldan JM, Garcia-Barroso C, Franco R, Aguirre N, fingertip ulcerations in a patient with scleroderma: Successful Garcia-Osta A. Sildenafil restores cognitive function without treatment with sildenafil. J Rheumatol. 2005; 32:2440–2442. affecting β-amyloid burden in a mouse model of Alzheimer’s 163. Impens AJ, Phillips K, Schiopu E. PDE-5 inhibitors in disease. Br J Pharmacol. 2011; 164:2029–2041. scleroderma Raynaud phenomenon and digital ulcers: 151. Puzzo D, Staniszewski A, Deng SX, Privitera L, Leznik E, Current status of clinical trials. Int J Rheumatol. 2011; Liu S, Zhang H, Feng Y, Palmeri A, Landry DW, Arancio O. 2011:392542. Phosphodiesterase 5 inhibition improves synaptic function, 164. Roustit M, Blaise S, Allanore Y, Carpentier PH, Caglayan memory, and amyloid-beta load in an Alzheimer’s disease E, Cracowski JL. Phosphodiesterase-5 inhibitors for the mouse model. J Neurosci. 2009; 29:8075–8086. treatment of secondary Raynaud’s phenomenon: Systematic 152. Goff DC, Cather C, Freudenreich O, Henderson DC, review and meta-analysis of randomised trials. Ann Rheum Evins AE, Culhane MA, Walsh JP. A placebo-controlled Dis. 2013; 72:1696–1699. study of sildenafil effects on cognition in Schizophrenia. 165. Fries R, Shariat K, von Wilmowsky H, Bohm M. Sildenafil Psychopharmacology (Berl). 2009; 202:411–417. in the treatment of raynaud’s phenomenon resistant to 153. Rutten K, Basile JL, Prickaerts J, Blokland A, Vivian JA. vasodilatory therapy. Circulation. 2005; 112:2980–2985. Selective PDE inhibitors rolipram and sildenafil improve 166. Brueckner CS, Becker MO, Kroencke T, Huscher D, object retrieval performance in adult cynomolgus macaques. Scherer HU, Worm M, Burmester G, Riemekasten G. Effect Psychopharmacology (Berl). 2008; 196:643–648. of sildenafil on digital ulcers in systemic sclerosis: Analysis 154. Koka S, Das A, Zhu SG, Durrant D, Xi L, Kukreja RC. from a single centre pilot study. Ann Rheum Dis. 2010; Long-acting phosphodiesterase-5 inhibitor tadalafil 69:1475–1478. www.impactjournals.com/oncotarget 99197 Oncotarget 167. Young A, Khanna D. Systemic sclerosis: A systematic 179. Mayer M, Stief CG, Truss MC, Uckert S. Phosphodiesterase review on therapeutic management from 2011 to 2014. Curr inhibitors in female sexual dysfunction. World J Urol. 2005; Opin Rheumatol. 2015; 27:241–248. 23:393–397. 168. Botha P, Parry G, Dark JH, Macgowan GA. Acute 180. Check JH, Graziano V, Lee G, Nazari A, Choe JK, hemodynamic effects of intravenous sildenafil citrate in Dietterich C. Neither sildenafil nor vaginal estradiol congestive heart failure: Comparison of phosphodiesterase improves endometrial thickness in women with thin type-3 and -5 inhibition. J Heart Lung Transplant. 2009; endometria after taking oral estradiol in graduating dosages. 28:676–682. Clin Exp Obstet Gynecol. 2004; 31:99–102. 169. Maruszewski M, Zakliczynski M, Przybylski R, Kucewicz- 181. Jerzak M, Kniotek M, Mrozek J, Gorski A, Baranowski Czech E, Zembala M. Use of sildenafil in heart transplant W. Sildenafil citrate decreased natural killer cell activity recipients with pulmonary hypertension may prevent right and enhanced chance of successful pregnancy in women heart failure. Transplant Proc. 2007; 39:2850–2852. with a history of recurrent miscarriage. Fertil Steril. 2008; 170. De Santo LS, Mastroianni C, Romano G, Amarelli C, 90:1848–1853. Marra C, Maiello C, Galdieri N, Della Corte A, Cotrufo 182. El-Far M, El-Motwally Ael G, Hashem IA, Bakry N. M, Caianiello G. Role of sildenafil in acute posttransplant Biochemical role of intravaginal sildenafil citrate as a novel right ventricular dysfunction: Successful experience in 13 antiabortive agent in unexplained recurrent spontaneous consecutive patients. Transplant Proc. 2008; 40:2015–2018. miscarriage: First clinical study of four case reports from 171. Austin MJ, McDougall NI, Wendon JA, Sizer E, Knisely Egypt. Clin Chem Lab Med. 2009; 47:1433–1438. AS, Rela M, Wilson C, Callender ME, O’Grady JG, 183. Sher G, Fisch JD. Vaginal sildenafil (viagra): A preliminary Heneghan MA. Safety and efficacy of combined use of report of a novel method to improve uterine artery blood sildenafil, bosentan, and iloprost before and after liver flow and endometrial development in patients undergoing transplantation in severe portopulmonary hypertension. IVF. Hum Reprod. 2000; 15:806–809. Liver Transpl. 2008; 14:287–291. 184. Sher G, Fisch JD. Effect of vaginal sildenafil on the 172. Cadden IS, Greanya ED, Erb SR, Scudamore CH, outcome of in vitro fertilization (ivf) after multiple ivf Yoshida EM. The use of sildenafil to treat portopulmonary failures attributed to poor endometrial development. Fertil hypertension prior to liver transplantation. Ann Hepatol. Steril. 2002; 78:1073–1076. 2009; 8:158–161. 185. George EM, Granger JP. Mechanisms and potential 173. Gough MS, White RJ. Sildenafil therapy is associated with therapies for preeclampsia. Curr Hypertens Rep. 2011; improved hemodynamics in liver transplantation candidates 13:269–275. with pulmonary arterial hypertension. Liver Transpl. 2009; 186. Turgut NH, Temiz TK, Bagcivan I, Turgut B, Gulturk S, 15:30–36. Karadas B. The effect of sildenafil on the altered thoracic 174. Hemnes AR, Robbins IM. Sildenafil monotherapy aorta smooth muscle responses in rat pre-eclampsia model. in portopulmonary hypertension can facilitate liver Eur J Pharmacol. 2008; 589:180–187. transplantation. Liver Transpl. 2009; 15:15–19. 187. Samangaya RA, Mires G, Shennan A, Skillern L, Howe 175. Lasaponara F, Sedigh O, Pasquale G, Bosio A, Rolle L, D, McLeod A, Baker PN. A randomised, double-blinded, Ceruti C, Timpano M, Negro CL, Paradiso M, Abbona placebo-controlled study of the phosphodiesterase type A, Segoloni GP, Fontana D. Phosphodiesterase type 5 5 inhibitor sildenafil for the treatment of preeclampsia. inhibitor treatment for erectile dysfunction in patients with Hypertens Pregnancy. 2009; 28:369–382. end-stage renal disease receiving dialysis or after renal 188. Hackett G. PDE5 inhibitors in diabetic peripheral transplantation. J Sex Med. 2013; 10:2798–2814. neuropathy. Int J Clin Pract. 2006; 60:1123–1126. 176. Pizanis N, Heckmann J, Wendt D, Tsagakis K, Jakob H, 189. Wang L, Chopp M, Szalad A, Liu Z, Bolz M, Alvarez FM, Lu Kamler M. Improvement of pulmonary microcirculation M, Zhang L, Cui Y, Zhang RL, Zhang ZG. Phosphodiesterase-5 after lung transplantation using phosphodiesterase-5 is a therapeutic target for peripheral neuropathy in diabetic inhibitor modified preservation solution. Eur J Cardiothorac mice. Neuroscience. 2011; 193:399–410. Surg. 2009; 35:801–806. 190. Wang L, Chopp M, Zhang ZG. PDE5 inhibitors promote 177. Tsai JW, Ayubi FS, Hart KL, Baur DA, Parham MA, Moon recovery of peripheral neuropathy in diabetic mice. Neural JK, Vazquez R, Chasen AB, Zhang Z, Pizarro JM. Evaluation Regen Res. 2017; 12:218–219. of the effect of sildenafil and vascular endothelium growth 191. Patil CS, Singh VP, Singh S, Kulkarni SK. Modulatory factor combination treatment on skin flap survival in rats. effect of the PDE-5 inhibitor sildenafil in diabetic Aesthetic Plast Surg. 2008; 32:624–631. neuropathy. Pharmacology. 2004; 72:190–195. 178. Kaya B, Cerkez C, Isilgan SE, Gokturk H, Yigman Z, Serel 192. Desouza C, Parulkar A, Lumpkin D, Akers D, Fonseca VA. S, Can B, Ergun H. Comparison of the effects of systemic Acute and prolonged effects of sildenafil on brachial artery sildenafil, tadalafil, and vardenafil treatments on skin flap flow-mediated dilatation in type 2 diabetes. Diabetes Care. survival in rats. J Plast Surg Hand Surg. 2015; 49:358–362. 2002; 25:1336–1339. www.impactjournals.com/oncotarget 99198 Oncotarget 193. Aversa A, Bruzziches R, Francomano D, Natali M, Lenzi A. 205. Chan DC, Earle KA, Zhao TL, Helfrich B, Zeng C, Baron Testosterone and phosphodiesterase type-5 inhibitors: New A, Whitehead CM, Piazza G, Pamukcu R, Thompson WJ, strategy for preventing endothelial damage in internal and Alila H, Nelson P, Bunn PA. Exisulind in combination with sexual medicine? Ther Adv Urol. 2009; 1:179–197. docetaxel inhibits growth and metastasis of human lung 194. Aversa A, Vitale C, Volterrani M, Fabbri A, Spera G, cancer and prolongs survival in athymic nude rats with Fini M, Rosano GM. Chronic administration of sildenafil orthotopic lung tumors. Clin Cancer Res. 2002; 8:904–912. improves markers of endothelial function in men with type 206. Bunn PA Jr, Chan DC, Earle K, Zhao TL, Helfrich B, Kelly 2 diabetes. Diabet Med. 2008; 25:37–44. K, Piazza G, Whitehead CM, Pamukcu R, Thompson W, 195. Pelliccione F, D’Angeli A, D’Andrea S, Barbonetti Alila H. Preclinical and clinical studies of docetaxel and A, Pezzella A, Necozione S, Falone S, Amicarelli F, exisulind in the treatment of human lung cancer. Semin Francavilla F, Francavilla S. Tadalafil treatment had a Oncol. 2002; 29:87–94. modest effect on endothelial cell damage and repair ability 207. Li Q, Shu Y. Pharmacological modulation of cytotoxicity markers in men with erectile dysfunction and vascular risk. and cellular uptake of anti-cancer drugs by PDE5 inhibitors Asian J Androl. 2014; 16:290–294. in lung cancer cells. Pharm Res. 2014; 31:86–96. 196. Grover-Paez F, Villegas Rivera G, Guillen Ortiz R. 208. Booth L, Roberts JL, Poklepovic A, Gordon S, Dent P. Sildenafil citrate diminishes microalbuminuria and the PDE5 inhibitors enhance the lethality of pemetrexed percentage of A1C in male patients with type 2 diabetes. through inhibition of multiple chaperone proteins and via Diabetes Res Clin Pract. 2007; 78:136–140. the actions of cyclic GMP and nitric oxide. Oncotarget. 197. Palit V, Eardley I. An update on new oral PDE5 inhibitors 2017; 8:1449–1468. http://doi.org/18632/oncotarget.13640. for the treatment of erectile dysfunction. Nat Rev Urol. 209. Hoang T, Kim K, Merchant J, Traynor AM, McGovern J, 2010; 7:603–609. Oettel KR, Sanchez FA, Ahuja HG, Hensing TA, Larson M, 198. Eardley I, Donatucci C, Corbin J, El-Meliegy A, Schiller JH. Phase I/II study of gemcitabine and exisulind Hatzimouratidis K, McVary K, Munarriz R, Lee SW. as second-line therapy in patients with advanced non-small Pharmacotherapy for erectile dysfunction. J Sex Med. 2010; cell lung cancer. J Thorac Oncol. 2006; 1:218–225. 7:524–540. 210. Jones SF, Kuhn JG, Greco FA, Raefsky EL, Hainsworth JD, 199. Nehra A. Erectile dysfunction and cardiovascular disease: Dickson NR, Thompson DS, Willcutt NT, White MB, Burris Efficacy and safety of phosphodiesterase type 5 inhibitors in HA, 3rd. A phase I/II study of exisulind in combination with men with both conditions. Mayo Clin Proc. 2009; 84:139– docetaxel/carboplatin in patients with metastatic non-small- 148. cell lung cancer. Clin Lung Cancer. 2005; 6:361–366. 200. Molina JR, Yang P, Cassivi SD, Schild SE, Adjei AA. 211. Masters GA, Li S, Dowlati A, Madajewicz S, Langer C, Non-small cell lung cancer: Epidemiology, risk factors, Schiller J, Johnson D. A phase II trial of carboplatin and treatment, and survivorship. Mayo Clin Proc. 2008; 83:584– gemcitabine with exisulind (IND #65,056) in patients 594. with advanced non-small cell lung cancer: an Eastern 201. Piazza GA, Alberts DS, Hixson LJ, Paranka NS, Li H, Cooperative Oncology Group Study (E1501). J Thorac Finn T, Bogert C, Guillen JM, Brendel K, Gross PH, Sperl Oncol. 2006; 1:673–678. G, Ritchie J, Burt RW, et al. Sulindac sulfone inhibits 212. Weiss GJ, Vokes EE, Bunn PA Jr, Magree L, Rusk J, Albert azoxymethane-induced colon carcinogenesis in rats without D, Kelly K. Docetaxel and exisulind in previously treated reducing prostaglandin levels. Cancer Res. 1997; 57:2909– non-small cell lung cancer (NSCLC) patients: A multicenter, 2915. phase II clinical trial. J Thorac Oncol. 2007; 2:933–938. 202. Thompson WJ, Piazza GA, Li H, Liu L, Fetter J, Zhu B, 213. Govindan R, Wang X, Baggstrom MQ, Burdette-Radoux S, Sperl G, Ahnen D, Pamukcu R. Exisulind induction of Hodgson L, Vokes EE, Green MR, Cancer and Leukemia apoptosis involves guanosine 3’,5’-cyclic monophosphate Group B. A phase II study of carboplatin, etoposide, and phosphodiesterase inhibition, protein kinase g activation, exisulind in patients with extensive small cell lung cancer: and attenuated beta-catenin. Cancer Res. 2000; 60:3338– CALGB 30104. J Thorac Oncol. 2009; 4:220–226. 3342. 214. Goluboff ET, Shabsigh A, Saidi JA, Weinstein IB, Mitra 203. Soh JW, Mao Y, Kim MG, Pamukcu R, Li H, Piazza N, Heitjan D, Piazza GA, Pamukcu R, Buttyan R, Olsson GA, Thompson WJ, Weinstein IB. Cyclic GMP mediates CA. Exisulind (sulindac sulfone) suppresses growth of apoptosis induced by sulindac derivatives via activation human prostate cancer in a nude mouse xenograft model by of c-JUN NH2-terminal kinase 1. Clin Cancer Res. 2000; increasing apoptosis. Urology. 1999; 53:440–445. 6:4136–4141. 215. Qian CN, Takahashi M, Kahnoski R, Teh BT. Effect of 204. Soriano AF, Helfrich B, Chan DC, Heasley LE, Bunn PA sildenafil citrate on an orthotopic prostate cancer growth Jr, Chou TC. Synergistic effects of new chemopreventive and metastasis model. J Urol. 2003; 170:994–997. agents and conventional cytotoxic agents against human 216. Das A, Durrant D, Mitchell C, Mayton E, Hoke NN, Salloum lung cancer cell lines. Cancer Res. 1999; 59:6178–6184. FN, Park MA, Qureshi I, Lee R, Dent P, Kukreja RC. www.impactjournals.com/oncotarget 99199 Oncotarget Sildenafil increases chemotherapeutic efficacy of doxorubicin 228. Wang X, Wang X, Liu T, He Q, Wang Y, Zhang X. in prostate cancer and ameliorates cardiac dysfunction. Proc Systematic review and meta-analysis of the use of Natl Acad Sci U S A. 2010; 107:18202–18207. phosphodiesterase type 5 inhibitors for treatment of erectile 217. Das A, Durrant D, Mitchell C, Dent P, Batra SK, Kukreja dysfunction following bilateral nerve-sparing radical RC. Sildenafil (viagra) sensitizes prostate cancer cells to prostatectomy. PLoS One. 2014; 9:e91327. doxorubicin-mediated apoptosis through CD95. Oncotarget. 229. Perou CM, Sorlie T, Eisen MB, van de Rijn M, Jeffrey SS, 2016; 7:4399–4413. http://doi.org/10.18632/oncotarget.6749. Rees CA, Pollack JR, Ross DT, Johnsen H, Akslen LA, Fluge 218. Liu N, Mei L, Fan X, Tang C, Ji X, Hu X, Shi W, Qian Y, O, Pergamenschikov A, Williams C, et al. Molecular portraits Hussain M, Wu J, Wang C, Lin S, Wu X. Phosphodiesterase of human breast tumours. Nature. 2000; 406:747–752. 5/Protein Kinase G signal governs stemness of prostate 230. Tinsley HN, Gary BD, Keeton AB, Zhang W, Abadi AH, cancer stem cells through hippo pathway. Cancer Lett. 2016; Reynolds RC, Piazza GA. Sulindac sulfide selectively 378:38–50. inhibits growth and induces apoptosis of human breast 219. Zenzmaier C, Sampson N, Pernkopf D, Plas E, Untergasser tumor cells by phosphodiesterase 5 inhibition, elevation of G, Berger P. Attenuated proliferation and trans- cyclic GMP, and activation of protein kinase G. Mol Cancer Ther. 2009; 8:3331–3340. differentiation of prostatic stromal cells indicate suitability of phosphodiesterase type 5 inhibitors for prevention and 231. Tinsley HN, Gary BD, Keeton AB, Lu W, Li Y, Piazza GA. treatment of benign prostatic hyperplasia. Endocrinology. Inhibition of PDE5 by sulindac sulfide selectively induces 2010; 151:3975–3984. apoptosis and attenuates oncogenic Wnt/β-catenin-mediated transcription in human breast tumor cells. Cancer Prev Res 220. Wang C. Phosphodiesterase-5 inhibitors and benign (Phila). 2011; 4:1275–1284. prostatic hyperplasia. Curr Opin Urol. 2010; 20:49–54. 232. Marino N, Collins JW, Shen C, Caplen NJ, Merchant AS, 221. Chavez AH, Scott Coffield K, Hasan Rajab M, Jo C. Gokmen-Polar Y, Goswami CP, Hoshino T, Qian Y, Sledge Incidence rate of prostate cancer in men treated for erectile GW Jr, Steeg PS. Identification and validation of genes dysfunction with phosphodiesterase type 5 inhibitors: with expression patterns inverse to multiple metastasis Retrospective analysis. Asian J Androl. 2013; 15:246–248. suppressor genes in breast cancer cell lines. Clin Exp 222. Khandrika L, Lieberman R, Koul S, Kumar B, Maroni P, Metastasis. 2014; 31:771–786. Chandhoke R, Meacham RB, Koul HK. Hypoxia-associated 233. Thompson HJ, Jiang C, Lu J, Mehta RG, Piazza GA, p38 mitogen-activated protein kinase-mediated androgen Paranka NS, Pamukcu R, Ahnen DJ. Sulfone metabolite receptor activation and increased HIF-1 alpha levels of sulindac inhibits mammary carcinogenesis. Cancer Res. contribute to emergence of an aggressive phenotype in 1997; 57:267–271. prostate cancer. Oncogene. 2009; 28:1248–1260. 234. Karami-Tehrani F, Moeinifard M, Aghaei M, Atri M. 223. Movsas B, Chapman JD, Greenberg RE, Hanlon AL, Evaluation of PDE5 and PDE9 expression in benign and Horwitz EM, Pinover WH, Stobbe C, Hanks GE. malignant breast tumors. Arch Med Res. 2012; 43:470–475. Increasing levels of hypoxia in prostate carcinoma correlate 235. Liu L, Li H, Underwood T, Lloyd M, David M, Sperl G, significantly with increasing clinical stage and patient age: Pamukcu R, Thompson WJ. Cyclic GMP-dependent protein an Eppendorf pO(2) study. Cancer. 2000; 89:2018–2024. kinase activation and induction by exisulind and CP461 in 224. Hamilton TK, Hu N, Kolomitro K, Bell EN, Maurice DH, colon tumor cells. J Pharmacol Exp Ther. 2001; 299:583–592. Graham CH, Siemens DR. Potential therapeutic applications 236. Whitt JD, Li N, Tinsley HN, Chen X, Zhang W, Li Y, Gary of phosphodiesterase inhibition in prostate cancer. World J BD, Keeton AB, Xi Y, Abadi AH, Grizzle WE, Piazza GA. Urol. 2013; 31:325–330. A novel sulindac derivative that potently suppresses colon 225. Goluboff ET, Prager D, Rukstalis D, Giantonio B, Madorsky tumor cell growth by inhibiting cGMP phosphodiesterase M, Barken I, Weinstein IB, Partin AW, Olsson CA, Network and β-catenin transcriptional activity. Cancer Prev Res UOR. Safety and efficacy of exisulind for treatment of (Phila). 2012; 5:822–833. recurrent prostate cancer after radical prostatectomy. J Urol. 237. Li N, Xi Y, Tinsley HN, Gurpinar E, Gary BD, Zhu B, Li 2001; 166:882–886. Y, Chen X, Keeton AB, Abadi AH, Moyer MP, Grizzle 226. Michl U, Molfenter F, Graefen M, Tennstedt P, Ahyai S, WE, Chang WC, et al. Sulindac selectively inhibits colon Beyer B, Budaus L, Haese A, Heinzer H, Oh SJ, Salomon G, tumor cell growth by activating the cGMP/PKG pathway to Schlomm T, Steuber T, et al. Use of phosphodiesterase type suppress Wnt/β-catenin signaling. Mol Cancer Ther. 2013; 5 inhibitors may adversely impact biochemical recurrence 12:1848–1859. after radical prostatectomy. J Urol. 2015; 193:479–483. 238. Tinsley HN, Gary BD, Thaiparambil J, Li N, Lu W, Li Y, 227. Gallina A, Bianchi M, Gandaglia G, Cucchiara V, Suardi Maxuitenko YY, Keeton AB, Piazza GA. Colon tumor cell N, Montorsi F, Briganti A. A detailed analysis of the growth-inhibitory activity of sulindac sulfide and other association between postoperative phosphodiesterase type nonsteroidal anti-inflammatory drugs is associated with 5 inhibitor use and the risk of biochemical recurrence after phosphodiesterase 5 inhibition. Cancer Prev Res (Phila). radical prostatectomy. Eur Urol. 2015; 68:750–753. 2010; 3:1303–1313. www.impactjournals.com/oncotarget 99200 Oncotarget 239. Rice PL, Goldberg RJ, Ray EC, Driggers LJ, Ahnen DJ. 03012 and Vagra treatment inhibits the activity of multiple Inhibition of extracellular signal-regulated kinase 1/2 chaperone proteins and disrupts the blood-brain barrier: phosphorylation and induction of apoptosis by sulindac Implications for anti-cancer therapies. J Cell Physiol. 2015; metabolites. Cancer Res. 2001; 61:1541–1547. 230:1982–1998. 240. Rice PL, Beard KS, Driggers LJ, Ahnen DJ. Inhibition of 251. Hu J, Ljubimova JY, Inoue S, Konda B, Patil R, Ding H, extracellular-signal regulated kinases 1/2 is required for Espinoza A, Wawrowsky KA, Patil C, Ljubimov AV, Black apoptosis of human colon cancer cells in vitro by sulindac KL. Phosphodiesterase type 5 inhibitors increase herceptin metabolites. Cancer Res. 2004; 64:8148–8151. transport and treatment efficacy in mouse metastatic brain 241. Mei XL, Yang Y, Zhang YJ, Li Y, Zhao JM, Qiu JG, Zhang tumor models. PLoS One. 2010; 5:e10108. WJ, Jiang QW, Xue YQ, Zheng DW, Chen Y, Qin WM, Wei 252. Wang R, Chen W, Zhang Q, Liu Y, Qiao X, Meng K, Mao MN, et al. Sildenafil inhibits the growth of human colorectal Y. Phosphodiesterase type 5 inhibitor tadalafil increases cancer in vitro and in vivo. Am J Cancer Res. 2015; 5:3311– rituximab treatment efficacy in a mouse brain lymphoma 3324. model. J Neurooncol. 2015; 122:35–42. 242. Li N, Chen X, Zhu B, Ramirez-Alcantara V, Canzoneri JC, 253. Cesarini V, Martini M, Vitiani LR, Gravina GL, Di Agostino Lee K, Sigler S, Gary B, Li Y, Zhang W, Moyer MP, Salter S, Graziani G, D’Alessandris QG, Pallini R, Larocca LM, EA, Wierzbicki A, et al. Suppression of β-catenin/TCF Rossi P, Jannini EA, Dolci S. Type 5 phosphodiesterase transcriptional activity and colon tumor cell growth by dual regulates glioblastoma multiforme aggressiveness and inhibition of PDE5 and 10. Oncotarget. 2015; 6:27403– clinical outcome. Oncotarget. 2017; 8:13223–13239. http:// 27415. http://doi.org/10.18632/oncotarget.4741. doi.org/10.18632/oncotarget.14656. 243. Stoner GD, Budd GT, Ganapathi R, DeYoung B, Kresty 254. Ferlay J, Soerjomataram I, Dikshit R, Eser S, Mathers C, LA, Nitert M, Fryer B, Church JM, Provencher K, Pamukcu Rebelo M, Parkin DM, Forman D, Bray F. Cancer incidence R, Piazza G, Hawk E, Kelloff G, et al. Sulindac sulfone and mortality worldwide: Sources, methods and major induced regression of rectal polyps in patients with familial patterns in Globocan 2012. Int J Cancer. 2015; 136:E359– adenomatous polyposis. Adv Exp Med Biol. 1999; 470:45– 386. 53. 255. Sherman SI. Thyroid carcinoma. Lancet. 2003; 361:501– 244. van Stolk R, Stoner G, Hayton WL, Chan K, DeYoung 511. B, Kresty L, Kemmenoe BH, Elson P, Rybicki L, Church 256. Schlumberger M, Lacroix L, Russo D, Filetti S, Bidart J, Provencher K, McLain D, Hawk E, et al. Phase I trial of JM. Defects in iodide metabolism in thyroid cancer and exisulind (sulindac sulfone, FGN-1) as a chemopreventive implications for the follow-up and treatment of patients. agent in patients with familial adenomatous polyposis. Clin Nat Clin Pract Endocrinol Metab. 2007; 3:260–269. Cancer Res. 2000; 6:78–89. 257. Qin C, Cau W, Zhang Y, Mghanga FP, Lan X, Gao Z, An R. 245. Islam BN, Sharman SK, Hou Y, Bridges AE, Singh N, Correlation of clinicopathological features and expression Kim S, Kolhe R, Trillo-Tinoco J, Rodriguez PC, Berger of molecular markers with prognosis after 131I treatment FG, Sridhar S, Browning DD. Sildenafil suppresses of differentiated thyroid carcinoma. Clin Nucl Med. 2012; inflammation-driven colorectal cancer in mice. Cancer Prev 37:e40–46. Res (Phila). 2017; 10:377–388. 258. Lakics V, Karran EH, Boess FG. Quantitative comparison of 246. Piazza GA. Validation of PDE5 as a chemoprevention phosphodiesterase mRNA distribution in human brain and target. Cancer Prev Res (Phila). 2017; 10:373–376. peripheral tissues. Neuropharmacology. 2010; 59:367–374. 247. Giordano D, Giorgi M, Sette C, Biagioni S, Augusti-Tocco 259. Persani L, Lania A, Alberti L, Romoli R, Mantovani G. cAMP-dependent induction of PDE5 expression in G, Filetti S, Spada A, Conti M. Induction of specific murine neuroblastoma cell differentiation. FEBS Lett. 1999; phosphodiesterase isoforms by constitutive activation of the 446:218–222. cAMP pathway in autonomous thyroid adenomas. J Clin 248. Roberts JL, Booth L, Conley A, Cruickshanks N, Malkin Endocrinol Metab. 2000; 85:2872–2878. M, Kukreja RC, Grant S, Poklepovic A, Dent P. PDE5 260. Sponziello M, Verrienti A, Rosignolo F, De Rose RF, inhibitors enhance the lethality of standard of care Pecce V, Maggisano V, Durante C, Bulotta S, Damante chemotherapy in pediatric CNS tumor cells. Cancer Biol G, Giacomelli L, Di Gioia CR, Filetti S, Russo D, et al. Ther. 2014; 15:758–767. PDE5 expression in human thyroid tumors and effects of 249. Black KL, Yin D, Ong JM, Hu J, Konda BM, Wang X, PDE5 inhibitors on growth and migration of cancer cells. Ko MK, Bayan JA, Sacapano MR, Espinoza A, Irvin DK, Endocrine. 2015; 50:434–441. Shu Y. PDE5 inhibitors enhance tumor permeability and 261. Caronia LM, Phay JE, Shah MH. Role of braf in thyroid efficacy of chemotherapy in a rat brain tumor model. Brain oncogenesis. Clin Cancer Res. 2011; 17:7511–7517. Res. 2008; 1230:290–302. 262. Spoto G, Esposito A, Santoleri F, Rubini C, Rutjes AW, 250. Booth L, Roberts JL, Tavallai M, Nourbakhsh A, Fioroni M, Ferrante M, Petrini M. Does cyclic guanosine Chuckalovcak J, Carter J, Poklepovic A, Dent P. OSU- monophosphate induce autophagy in thyroid malignant www.impactjournals.com/oncotarget 99201 Oncotarget carcinoma through down-regulation of cyclic guanosine 272. Wang J, Shen Y, Wang J, Xue Y, Liao L, Thapa S, Ji K. monophosphate phosphodiesterase? J Biol Regul Homeost Relation of phosphodiesterase type 5 inhibitors and Agents. 2016; 30:599–604. malignant melanoma: A meta-analysis and systematic 263. De Rose RF, Celano M, Maggisano V, Vero A, Di review. Oncotarget. 2017; 8:46461–46467. http://doi. Francesco M, Paolino D, Russo D. PDE5 inhibitors-loaded org/10.18632/oncotarget.17518. nanovesicles: Physico-chemical properties and in vitro 273. Ren Y, Zheng J, Yao X, Weng G, Wu L. Essential role antiproliferative activity. Nanomaterials. 2016; 6:1–12. of the cGMP/PKG signaling pathway in regulating the 264. Cummins DL, Cummins JM, Pantle H, Silverman MA, proliferation and survival of human renal carcinoma cells. Leonard AL, Chanmugam A. Cutaneous malignant Int J Mol Med. 2014; 34:1430–1438. melanoma. Mayo Clin Proc. 2006; 81:500–507. 274. Zenitani M, Nojiri T, Uehara S, Miura K, Hosoda H, 265. Sulaimon SS, Kitchell BE. The basic biology of malignant Kimura T, Nakahata K, Miyazato M, Okuyama H, Kangawa melanoma: Molecular mechanisms of disease progression K. C-type natriuretic peptide in combination with sildenafil and comparative aspects. J Vet Intern Med. 2003; 17:760– attenuates proliferation of rhabdomyosarcoma cells. Cancer 772. Med. 2016; 5:795–805. 266. Murata T, Shimizu K, Watanabe Y, Morita H, Sekida M, 275. Sarfati M, Mateo V, Baudet S, Rubio M, Fernandez C, Tagawa T. Expression and role of phosphodiesterase 5 Davi F, Binet JL, Delic J, Merle-Beral H. Sildenafil and in human malignant melanoma cell line. Anticancer Res. vardenafil, types 5 and 6 phosphodiesterase inhibitors, 2010; 30:355–358. induce caspase-dependent apoptosis of B-chronic 267. Arozarena I, Sanchez-Laorden B, Packer L, Hidalgo- lymphocytic leukemia cells. Blood. 2003; 101:265–269. Carcedo C, Hayward R, Viros A, Sahai E, Marais R. 276. Kumazoe M, Kim Y, Bae J, Takai M, Murata M, Suemasu Y, Oncogenic BRAF induces melanoma cell invasion by Sugihara K, Yamashita S, Tsukamoto S, Huang Y, Nakahara downregulating the cGMP-specific phosphodiesterase K, Yamada K, Tachibana H. Phosphodiesterase 5 inhibitor PDE5A. Cancer Cell. 2011; 19:45–57. acts as a potent agent sensitizing acute myeloid leukemia 268. Dhayade S, Kaesler S, Sinnberg T, Dobrowinski H, cells to 67-kDa laminin receptor-dependent apoptosis. Peters S, Naumann U, Liu H, Hunger RE, Thunemann FEBS Lett. 2013; 587:3052–3057. M, Biedermann T, Schittek B, Simon HU, Feil S, et al. 277. Kumazoe M, Tsukamoto S, Lesnick C, Kay NE, Yamada Sildenafil potentiates a cGMP-dependent pathway to K, Shanafelt TD, Tachibana H. Vardenafil, a clinically promote melanoma growth. Cell Rep. 2016; 14:2599–2610. available phosphodiesterase inhibitor, potentiates the 269. Li WQ, Qureshi AA, Robinson KC, Han J. Sildenafil killing effect of EGCG on CLL cells. Br J Haematol. 2015; use and increased risk of incident melanoma in US men: 168:610–613. a prospective cohort study. JAMA Intern Med. 2014; 278. Noonan KA, Ghosh N, Rudraraju L, Bui M, Borrello I. 174:964–970. Targeting immune suppression with PDE5 inhibition in 270. Loeb S, Folkvaljon Y, Lambe M, Robinson D, Garmo end-stage multiple myeloma. Cancer Immunol Res. 2014; H, Ingvar C, Stattin P. Use of phosphodiesterase type 5 2: 725–731. inhibitors for erectile dysfunction and risk of malignant 279. Califano JA, Khan Z, Noonan KA, Rudraraju L, Zhang melanoma. JAMA. 2015; 313:2449–2455. Z, Wang H, Goodman S, Gourin CG, Ha PK, Fakhry C, 271. Matthews A, Langan SM, Douglas IJ, Smeeth L, Bhaskaran Saunders J, Levine M, Tang M, et al. Tadalafil augments K. Phosphodiesterase type 5 inhibitors and risk of malignant tumor specific immunity in patients with head and neck melanoma: matched cohort study using primary care data squamous cell carcinoma. Clin Cancer Res. 2015; 21: from the UK clinical practice research datalink. PLoS Med. 30–38. 2016; 13:e1002037.

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